Thursday, 29 August 2013

Question 78 – The Specific Powers of the Soul

Why this Question Matters

After discussing the powers of the soul in general in Ia.q77, Aquinas now turns to specifics. The theologian is mostly concerned with the intellective and appetitive powers of the soul because that is where the virtues are to be found; a topic of central importance in the second part of the summa. However, one must have at least a basic appreciation of the other powers of the soul as the intellective and the appetitive depend upon these in a number of ways. So, in this question Aquinas will consider those powers of the soul that are preparatory for intellective understanding. The next question will be dedicated to the intellect and the following four questions (1a.q80-83) to the appetitive powers.

This question is therefore dedicated to a classification of the powers of the soul into kinds and then to discussions of the vegetative powers of the soul and then the interior and exterior senses that make up the sentient part of the soul.

The Thread of the Argument

A1: We’ve already seen a division of the powers of the soul into the vegetative, the sentient and the intellective. There are other ways of classifying these powers; indeed the second objection identifies a classification into four ways of living (modi vivendi). However, what Aquinas is concerned with in this question is to divide the powers of the soul according to their objects. Under this classification we identify the vegetative, the sentient, the appetitive, the locomotive and the intellective.

Aquinas identifies these five powers of the soul claiming that three of them can justly be called souls and four of them ways of living. The division into the vegetative, the sentient and the intellective arises from the three different ways in which powers of the soul can exceed the powers of an ordinary corporeal body. The intellective power is not exercised through a corporeal body at all; the sentient power works through corporeal organs but requires incorporeal organization of the senses into a whole; and the vegetative power works through a body and by a body.

When we turn to a consideration of the powers of the soul seen from the point of view of their objects, however, we see more than just these. We should not be surprised that the more universal the object, the higher the power; we can see a three step ordering to the type of object that the soul can have. In the first place, the vegetative powers of the soul have the body with which it is united as their only object; they are there in order to maintain the good functioning of that body. The second kind of power possessed by the soul has to do with objects that are sensed; the third kind of power has a more universal object, that of being in general. However, we must notice that each of these latter two kinds of power (the sentient and the intellective) possesses two distinct components. The first type of component corresponds to the forming of some sort of similitude to the external object within the soul and the second type of component corresponds to a movement towards this external object. For the first component, the sentient powers form a similitude of a particular external object and the intellective powers use the similitude in grasping the universality of the object. For the second component, there are two powers of the soul that correspond to the movement of the soul towards the object of perception. The appetitive powers specify the external object as an end and the locomotive powers move towards that end.

Following Aquinas’s top-down ordering of material in his consideration of human nature, this may sound quite abstract, so let’s take an example. The sentient powers identify that there is a cream cake on the table; the intellective powers recognize the individual cream cake as being a cream cake in general; the vegetative powers sit there grumbling away informing the intellective powers that the body is hungry; therefore the intellective powers specify the cream cake as a good to the appetitive powers which kick the locomotive powers into action to go get and eat the cream cake.

Finally, when we consider the ways in which something can be alive, we recognize beings such as plants in which only the vegetative is present, immobile animals in which the sentient is also present, mobile (or perfect) animals in which the power to effect movement from place to place is present and human beings in which the intellective powers are also present.

The third objection suggested that since an appetitive power automatically goes with each of the powers of the soul it is wrong to identify it as separate from that corresponding power. In answer, Aquinas argues that entities have natural appetites that order them towards what is fitting for them. The sense of sight, for example, has a natural inclination towards the visible. But in an animal the whole is more than the sum of the parts; there needs to be more than just the sum of the natural appetites of the components to explain the appetite of the animal. The animal apprehends an object in a number of ways though the sentient power, but the intellective power puts these images together into a single similitude that is then apprehended as a sort of composite. If this apprehended composite is to be desired by the animal, there needs to be some sort of overarching appetitive power.

A2: In the first article we saw that the vegetative parts of the soul have as object the body itself considered as a living being. We can discern a division into three operations within the vegetative soul: the first operation is that associated with giving being to the body; the second is to do with the body arriving at its appropriate size; and the third is to do with the body remaining in being, at its appropriate size. These three operations within the vegetative soul are called the generative, the augmentative and the nutritive respectively.

There is a division even among these three operations: the augmentative and the nutritive are concerned with the development and maintenance of the body itself, whereas the generative is concerned with the generation of a new individual. Aquinas considers that this difference raises the generative power to a greater excellence than the other two powers.

As the third objection argues, one might think l; that the augmentative and the nutritive should not be considered separate powers, but Aquinas insists that the feature of living beings whereby they start small and grow to their adult form is precisely special to living things. Therefore it is appropriate to identify a power of the soul responsible for this development that is differentiated from simple maintenance.

A3: In this article and the next Aquinas discusses the external and internal senses. Broadly speaking, the five external senses are concerned with sensation and the four internal senses are concerned with the perception of that sensation below the level of the intellect. These articles both ask the same question: are the respective sensory powers appropriately distinguished?

In the case of the exterior sensory powers, we all know about the senses of sight, hearing, smell, touch and taste; but why do we classify them this way? Aquinas lists a number of ways of looking at the classification of the senses that he considers inadequate: they could be classified through the organ that does the sensing; through the medium by which the senses come to sense something; or through a classification of the complexity of what is sensible. Rather than these, Aquinas wants to consider the senses under the notion of what is proper or per se to the sensory power itself. The idea is that nature has disposed the powers of the soul such that an intellectual creature with sensory powers can determine the natures of all sensible qualities. Therefore the sensory powers are distinguished from one another in a way that corresponds to the actual diversity of such objects.

A little terminology is required at this point. A proper sensible like sound or colour affects primarily only one sense. A common sensible can be sensed by a number of the senses. There are five common sensibles: size, shape, number, motion and rest. Both proper and common sensibles are per se sensibles. The per se sensibles are what the sensory powers actually sense. We must mention that there is also the notion of a per accidens sensible, but this is something that involves the intellect. For example, we “sense” the bodily substance that underlies the redness of the apple that we directly sense; we sense the anger in the person that we have upset. In summary, proper per se sensibles are the objects of the exterior senses.

Having arrived at the basis for classification, Aquinas considers it obvious in the light of experience that the external senses are what we commonly understand them to be. He now takes the opportunity to discuss their function in more detail. When a form like hotness is received in a body, the body actually gets hot: this is an example of a natural change. On the other hand, when the form of redness is received in the eye, the eye doesn’t actually go red: the way that the eye receives a form is different from the way in which a body receives the form of hotness. Aquinas calls this type of change a spiritual change. Aquinas observes that when a sensory organ receives a form there is a combination of natural change and spiritual change that depends upon the particular organ. Given his love of hierarchical organization, it will not surprise us to see that Aquinas considers those senses where the ratio of spiritual to natural change is highest to be superior. However, the science of the time rather lets him down in saying that there is no natural change in the sense of sight! Taking sight as an example, we would now say that there is a natural change in the rods and cones of the eye that accompanies the spiritual change of actually receiving the form of what is seen.

A4: The exterior sensory powers are responsible for the primary apprehension of the sensible qualities of objects. However, the mere sensing of these sensibles is not sufficient for their perception. In addition to the exterior sensory powers, we also have interior sensory powers that facilitate that perception. One must therefore ask how many of these interior sensory powers do we have and what are they? Now, Aquinas is, as a theologian, mostly concerned with the human animal in this treatise, but what he says about perception also applies to sufficiently complex non-human animals (which he calls perfect animals).

The first observation to be made is that the exterior sensory powers each sense their own proper objects: the eye senses patches of colour; the sense of smell detects an odour, and so forth. But there has to be some sort of power that integrates these exterior senses together, otherwise we would not perceive a red rose but simply the components out of which it is made. The interior sense responsible for this integration is the common sense.

Next we observe that animals not only perceive things when they are directly present to the exterior senses, they are also able to make a sense-image of an object when it is absent to the exterior senses. The power that enables the higher animals to do this is called the imagination or the power of imaging. It is in the imagination that a phantasm of a (present or absent) external object is formed. This latter is an intentional sensible form of the thing perceived. By this is meant that the phantasm is the form of the object perceived as it exists in the soul; it does not inform matter so becoming the actual object perceived, rather it has a special sort of intentional existence in the soul. For things currently perceived, the imagination completes the action of the common sense. It is also, especially in humans, capable of re-arranging and re-organizing the data given it by the common sense; perhaps it is in this that it is closest to what we commonly tend to call the imagination.

Animals are able to form what we call an instinctive judgement at the level of perception (rather than at the level of the intellect) as to whether a perceived object is likely to be good for it or to pose a danger. In order to do this it has to have access to what Aquinas sometimes calls insensate intentions which are forms not currently present to the senses but which allow the animal, by comparison, to come to a estimation of the benefit or risk posed by what is currently being perceived. The internal sensory power that performs the comparison is called the estimative power and the power that allows the animal to retain the insensate intentions is called the power of remembering or memorative power.

Hence, putting this all together, we can see that there are four internal sensory powers: the common sense, the imagination, the estimative power and the power of memory. However, when we consider specifically the human animal, we can see that more is to be said about the estimative power and the power of memory. For the estimative power, humans don’t just depend on inbuilt instinct; they have their intellects which enable them to put an individual object into the context of a universal and to make comparisons based on that context. “Lion” is a rather scary universal concept and “this particular lion” is an example of one of them that looks pretty fierce; I had better run for it. In humans, the estimative power is usually called the cogitative power (or particular reason) in contrast to the natural estimative power of non-human animals. Similarly, in humans the power of remembering is enhanced by our intellectual ability to reason in a syllogistic manner with the data held in the sense-memory. For this reason the sense of remembering is often called the sense of reminiscence in humans.

Handy Concepts

  • Aquinas is aiming for a description of knowledge in which there is some kind of union of the knowing subject with the external object. There is a perfection of the subject in “becoming” the thing known; a form (the soul) receives further forms, that which is actual receives a further actuality. One might recall at this point Aristotle’s assertion in de anima that the soul can “become all things”. We come to know an object through forms that are received and formed in the soul. Much of the rest of this treatise is devoted to working out how this all fits together.
  • The external senses each sense particular aspects about an object of perception, each receiving a particular form in a spiritual rather than natural way. The internal common sense integrates the forms received by the individual external senses and together with the imagination forms a phantasm, which is an intentional sensible form. The cogitative sense works upon data obtained from the common sense when the object is present or from the imaginative sense when it is absent. The power of memory obtains its data from the cogitative sense.
  • We will soon see that the phantasm is the basic data about an individual subject from which the intellectual powers of the soul abstract the quiddity of the object of perception, forming a universal concept of that object.
  • The word intentional comes from the Latin intendere, which means to reach out to or to point towards. Intentional forms in the soul point to the object to which they correspond. Intentional forms are often described as species. The terminology is reasonable as species specify their object.
  • In sensation the forms received by the soul are the forms corresponding to an individual object; they are limited by the matter of the object that they inform. We will see in the forthcoming questions that the intellect abstracts universal forms from these particular forms.


  • Aquinas uses the term common sense (sensus communis) in a way quite different to how we use it. For us it refers to knowledge that everyone should have; for Aquinas it is the power of the soul that unifies the individual senses.
  • One should note that common sensibles are not the object of the common sense. Common sensibles are sensed by the individual external senses and the data corresponding to them is re-assembled by the common (internal) sense. Thus the relations between common sensibles and the common sense is indirect.
  • In the fourth article, Aquinas seems to restrict the power of memory to something very specific; indeed he does. It’s important to keep in mind that he is concerned with sensation and perception in this question and not questions of intellect and will. We will soon see that what we consider as memory is actually one of the functions of the passive intellect.

Wednesday, 28 August 2013

The Aquinas Institute Opera Omnia Project

For those of you who like collecting Aquinas translations, I thought I'd put in a link to the Aquinas Institute's web page for the Opera Omnia project.

I don't (yet) have their translation of the summa theologiae, which I understand to be a re-working of the older Dominican translation, but I do have the commentaries on the letters of St Paul. I can attest that all aspects of the book production are of the very highest quality: a nice layout of Latin and English, printed on good quality paper and well bound. For what they are, the prices being asked are very modest.

Monday, 19 August 2013

Question 77 – The Powers of the Soul in General

Why this Question Matters.

In Thomistic psychology the soul has a number of powers that enable human beings to do various things. Aquinas will identify these powers under five headings in the next question. They are the vegetative, the sentient, the appetitive, the motive and the intellective powers. These powers are not quantitative parts of the soul in the sense that the soul is divided up into bits each of which performs various functions, but rather they are power parts of the soul. Before turning to the division of the powers of the soul into these five groups and before discussing each group in turn in the following questions, Aquinas must discuss what he means by a power of the soul and what these powers are in general.

The Thread of the Argument

A1: An obvious starting point might seem to be that the soul is nothing other than the collection of powers that it gives to the human being; the essence of the soul is its powers. After all, if we think in terms of substance and accidents, if the soul is not substantial then that would appear to make it accidental; and that doesn’t seem right at all.

We must note that the Latin word potentia is translated into English in a number of ways; in particular it is translated as potentiality (as in the division of being into actuality and potentiality) but it is also translated as power. There’s a strong etymological force suggesting that a power to do something is a potentiality towards some actuality. With that in mind, we turn towards Aquinas’s two arguments against the proposition that the essence of a soul is the soul’s powers.

In the first place, actuality and potentiality divide being; but more particularly, they divide being in every genus. This means that every pair of actuality and potentiality has to be referred to the same genus. So, if some actuality is in a certain genus, then its corresponding potentialities have to be in the same genus. Now, we have seen that the actuality of the soul is not in the genus of substance, therefore neither can any potentialities of the soul be in the genus of substance. Hence the power (potentia) of the soul cannot be the essence of the soul. Indeed, it is only for God that operation, power and essence coincide. We saw a similar argument when considering the angels in Ia.q54.a3.

The second argument is that if the soul’s essence were the immediate principle of its operation, then the soul would always be doing everything that souls do, as its powers would be in actuality. In the case of animating, this is fine; the possession of an animating soul makes the possessor to be alive at all times the soul is possessed. For other powers of the soul, this is less satisfactory. In particular, the soul is always in potentiality to some further actuality. When we learn to speak French, we are actually able to speak French but we are in potentiality to be actually speaking French at this moment. The technical way of describing this situation is that the soul is a first actuality (being able to speak French) ordered towards various second actualities (actually speaking French right now). This ability to be in potentiality to some further actuality is not therefore because of the soul’s essence but because of the soul’s power. Quoting from Aristotle’s de anima, Aquinas states that the soul is “the actuality of a body having life in potentiality”.

In answer to the objection that if the powers of the soul are not substantial they must be accidental, Aquinas answers that they can be considered accidental. If one is thinking strictly in terms of the division between substance and accidence as laid out in Aristotle’s Categories, then the powers of the soul lie in the second species of quality. However, we can also think of being an accident in terms of the five predicables (Aquinas calls them the five universals), genus, difference, species, property and accident. These five predicables are the logical equivalent of the universal concepts that the mind extracts from its perception of reality; they are the fundamental ways in which we can talk about that reality. When we think in terms of the predicables, then the powers of the soul are not accidents but rather are properties; they are among those things that do not belong to the essence of the soul but which are necessary consequences of the soul’s essential principles. In this sense we can consider the powers of the soul (and properties or proper accidents in general) to lie between the notion of substance and accident.

A2: Are the powers of the soul a unity, or does it make more sense to consider them as having some sort of distinguishability? Aquinas argues that it is most fitting to think of the powers of the soul in the plural. He makes an argument for this position based on the hierarchy of being: the higher one is up the hierarchy of being, the more unified are ones operations. Now man is at the pinnacle of material being and can achieve universal and perfect goodness in the beatific vision; things below man achieve what they achieve though a small number of distinct powers. But equally, man is at the lowest point of the hierarchy of spiritual beings. Therefore his spiritual operations are achieved by a plurality of powers in contrast to the supreme spiritual being, God, in whom there is a single power corresponding to His essence.

A3: Having established that there must be a plurality of powers in the soul, we must now enquire into how one may distinguish between these powers. The obvious (and correct) answer is that we distinguish between powers of the soul by means of the objects of those powers. However, some care has to be taken: we would not, for example, argue that there are separate powers corresponding to the perception of red things and green things. Rather, we must recognize that the powers are organized in such a way that there are objects that correspond per se to them. Things that we see and things that we hear certainly divide the sensory power into the sense of sight and the sense of hearing respectively; but we would not divide these senses further than that. Each power has a unitary aspect to it and the classes of objects that differentiate the powers of the soul correspond to this unity.

One might worry that the common sense (that power of the soul that unifies what is gathered by the individual senses) would provide a counter example to this classification. After all, things that are the object of the sense of sight are also the object of the common sense. But Aquinas is quite happy for there to be a hierarchy of objects: the object of the sense of sight is the visible sensible, but the object of the common sense is the sensible in general.

A4: The powers of the soul can be distinguished, but it makes sense to recognize an ordering between them. In order to show this Aquinas describes three ways in which there could be an ordering between powers; two of these types of ordering are to do with the dependence of powers on each other and the third is associated with the ordering between the objects of the powers.

For the first type of ordering where the order depends upon the perfect being prior to the imperfect (or to those things that are being perfected) the intellective powers are prior to the sentient powers and the sentient powers are prior to the nutritive powers as the former of each pair directs the latter. The second type of ordering occurs especially when we think temporally; the perfect tends to arise out of the imperfect. From this point of view, the nutritive is prior to the sentient as it is the former that gives rise to the generation of the latter; and the sentient is prior to the intellective in the sense that the intellect couldn’t do much without the senses.

When we consider ordering the powers of the soul according to their objects we can identify, for example in the senses, that some powers are naturally prior to others. Sight would seem to be prior to hearing and hearing prior to the sense of smell.

A5: We’ve seen that the human intellect is immaterial in the sense that it does not depend upon matter for its operation. This means that it is perfectly reasonable to attribute the human intellect, as a power of the soul, to the soul as a subject. Aquinas recognizes, however, that other powers of the soul depend critically on the body for their operations; the senses being clear examples. Therefore those powers of the soul that depend upon matter for their operations are in the body/soul combination as a subject rather than simply in the soul. The teaching of this article amplifies Aquinas’s argument that the human being by nature is a combination of soul and body and that to identify the human with the soul alone is incorrect.

A6: In the first article of this question we saw Aquinas arguing that the powers of the soul are accidents of a certain sort when considered in the context of the division of being (from the Categories) into substance and accidents; but that considered from the point of view of the predicables they can be thought of as properties. Aquinas now elevates this observation to its own article and takes the opportunity to give a mini tutorial on substance and accidents.

A substantial form is what makes something to exist in an absolute sense; one can only think of the being of the thing before it receives substantial form as a sort of being-in-potentiality. On the other hand, an accidental form makes something to exist in a certain way. An accidental form does not give being absolutely speaking to something; the subject of an accidental form already has existence through its substantial form. So, actuality is found in the substantial form (ontologically) prior to being found in its subject and the substantial form can be considered to cause being in its subject. By contrast, the actuality of the accidental form is caused by the actuality of the subject in which it inheres. So, the existing subject is in potentiality to receive an accidental form but it is also productive of the actuality of the accidental form.

All of the soul’s powers, whether they inhere in the soul alone as subject or in the body/soul composite, flow from the soul’s essence as their principle. Therefore the powers of the soul are proper accidents of the soul (in the language of the Categories) or properties (when considered as predicables).

A7: In the fourth article we saw that ordering is possible between the powers of the soul. We can take this further in order to argue that some powers of the soul can be seen as explanatory causes of others. As in the fourth article, this can be seen from two different directions. We can see the powers of the soul that are prior in the order of perfection to be prior in the order of causality in the sense of providing the less perfect powers with ends. The sensory powers exist for the sake of the intellect and not vice-versa, for example. Taken the other way around, we can think of the sentient powers of the soul as being material causes of the intellect insofar as without them, the intellect couldn’t do much.

A8: What happens at death when the soul is separated from the body? We have seen that the human soul is a subsistent form, so that it continues in existence after death; but what powers are left to this separated soul? One might argue, for example, that the powers of the soul must remain with the soul after death as these powers are properties of the soul. But on the other hand, we have also seen that although all the powers of the soul have the soul as their principle, they do not all inhere in the soul as in a subject; some inhere in the body/soul composite. Indeed, this is the criterion by which we can determine which powers remain and which lapse; those powers that inhere in the soul as a subject remain after the separation of the soul from the body, those which do not, do not. For the latter, their subject has been destroyed and they only remain in the soul virtually. In reply to the objection that the powers of the soul are properties of the soul, Aquinas insists that they are properties of the composite.

Handy Concepts

  • The five predicables, (genus, difference, species, property and accident), are the logical equivalent of the universal concepts that the mind extracts from its perception of reality; they are the fundamental ways in which we can talk about that reality.
  • In the seventh article Aquinas seems to be straining the meaning of the word cause. Banish Hume and understand causality in its relation to intelligibility; a cause is something that explains a state of affairs.
  • Aquinas’s reply to the first objection of the eight article shows that medieval philosophers didn’t canonize every text that they received as authoritative.
  • Although Aquinas doesn’t mention the general resurrection in the eighth article, surely he has in his mind the idea that the virtual powers of the soul corresponding to the powers that inhere in the body/soul composite as a subject will be restored to actuality at that point.


  • In the third article, Aquinas distinguishes between the powers of the soul by reference to their objects. He is careful to note that some classes of object (such as different colours) go together as the per se object of a single sense (in this case, the visual sense). If we inspect this example of the visual sense then we might ponder the modern understanding of the physiology of vision. This shows that the eye has rod cells that detect light at low levels, but which give rise only to a monochromatic perception; and cone cells that come in three classes, giving rise to the perception of red, blue and green respectively. Would this information incline use to consider the sense of sight as a compound of more primitive senses each with their per se objects integrated by a “common visual sense”?
  • The ordering of the powers of the soul (in the fourth article), especially from the point of view of their objects, may seem a little restrictive when we consider the modern notion of positive and negative feedback loops.

Sunday, 18 August 2013

50,000th Birthday

Last night this blog went over 50,000 page views! We are currently running at about 100 page views per day. Most of the traffic is coming from the United States, but many other countries are represented.

Thank you to everyone who visits; I hope that you gain something from your stay here!

Friday, 16 August 2013

Question 76 – The Union of the Soul with the Body

Why this Question Matters

Aquinas defined the soul to be the first principle of life in living things and devoted Ia.q75 to considering the soul in itself. Now it is time for him to turn to a consideration of how the soul and the body are united. The answer to this question is that the soul is the substantial form of the body; in a way the demonstration of this is simply a matter of definition within the metaphysical system that he has chosen. The challenge in this question is to show that such an approach makes for a coherent whole and that alternative approaches do not. At the time Aquinas was writing and for a period of years after his death, these sorts of questions were highly controversial. In time, Aquinas’s view was seen to be the correct one and later ecumenical councils of the church identified the approach that he took with part of the deposit of faith of the church.

The Thread of the Argument

A1: We’ve already seen that Aquinas claims that the soul is the form of the body; here he turns to a formal consideration of this question. Aquinas’s answer reiterates what he has already said: nothing acts except insofar as it is actually such-and-such, and that by which it is actually such-and such is precisely its form. What distinguishes living things from the inanimate are their vital operations; the soul is the ultimate internal principle of those vital operations. Once one has taken on-board those fundamental compositions of matter/form, potentiality/actuality and being/essence that lie at the heart of Aquinas’s metaphysics, the idea that the soul is the form of the body really becomes a matter of definition: the body must have a form that explains its fundamental operations; the soul is just what we call that form. The real content of an enquiry into the soul becomes an enquiry into what the soul is and does as a form.

Although Aquinas’s direct answer to the question posed by the article is quite short, the article itself is rather long! The reason for this is that Aquinas takes this opportunity to address the faults of a number of alternative theories about the relationship between the soul and the body. He does this in the remainder of the body of his answer and in his replies to the objections.

In pursuing this ambition, Aquinas starts off by inferring that which someone who claims that the soul is not the form of the body would have to concede about the relationship between soul and body. To do this, he makes a turn to the subject of intellectual understanding: intellectual understanding is not just something that happens out there, it’s something that belongs to each individual human. Socrates experiences that it is he himself who understands. There are three possibilities for the way in which intellection can be attributed to an individual human: the whole person can be doing the intellection (ruled out by Ia.q74.a4); per accidens (which is clearly nonsense); and through a part of the human being. This latter is the only feasible option, so if we grant that the soul is the principle of intellectual understanding in each individual, then we must allow that intellection is attributed to a part of that person and hence the soul is part of the person. The question then becomes how that part is united to the body.

Aquinas attributes to Averroes (Ibn Rushd, the Spanish Muslim philosopher known as “the Commentator” in the middle ages) the idea that the union between soul and body is effected by the intelligible species. We recall that these are what the active part of the intellect abstracts from the phantasms of the imagination for impression onto the passive part of the intellect. The idea is that phantasms are inherently bodily (produced by the sense organs), the passive part of the intellect is part of the soul and therefore the intellectual species act as the “glue” between the body and the soul. Aquinas finds fault with this, claiming that this explanation is not sufficient to account for the subjective nature of intellection: it simply doesn’t explain Socrates’s intellection as an action of the person of Socrates. Aquinas makes the analogy with sensation: the intelligible species exist in the passive intellect as visual sensations exist in the visual power. But the existence of visual sensations in the visual power does not explain the subjective experience of seeing; likewise the existence of the intelligible species in the passive intellect does not explain the experience of intellection of those species. As Aquinas puts it, the existence of the intelligible species in the passive intellect explains that the corresponding phantasms are understood, but not that Socrates understands.

Aquinas then turns to the opinion that the soul is united to the body as a mover in such a way that the action of the intellect can be attributed to the union. He finds several faults with this point of view. For example, the intellect does move the body, but it moves the body through an appetite which itself presupposes the action of the intellect. Socrates does not understand because he is moved by the intellect; rather he is moved because he understands. Similarly, Aquinas argues that attribution of the action of the intellect to the union of a part with the rest implies that the union cannot be considered as a unitary whole.

The objections to this article all hinge on a too narrow understanding of form and of how a form may enter into composition with matter. If we think of a natural object like a rock or of an artefact like a house, then when such objects go out of existence, their forms go out of existence as well. But the human soul is subsistent; it does not go out of existence when the body dies. Natural forms give a determinate existence to their matter/form composite, but the human intellect is able to grasp the quiddity of all things, which is something thoroughly indeterminate. For a natural object a form is what gives it esse; it is that by which the object exists. So it seems that esse does not belong to the form itself. These objections are fundamentally to do with what a form can be; in particular, the human soul is both subsistent and communicates the ability to the body to be in a state of indeterminacy as to the actual objects of cognition. Aquinas’s answers to these objections amount to pretty much the same thing: the fact of the existence of the intellect in human beings and the fact that this must have an ultimate internal explanation show that forms can indeed have these sorts of properties. Perhaps Aquinas’s task here has been made easier by the fact that he has already considered the angels; although the existence of the angels is a matter of faith, the fact that their existence is amenable to metaphysical explanation provides the materials to show that the spiritual human soul is also amenable to such explanation.

A2: A powerful idea at the time of Aquinas, and one which went on to have much influence after his death, was the idea of monopsychism; that humans share in one single intellectual soul. A component of what was known as Averroism, it provides a simple explanation for the fact that separate humans appear to have common perception and cognition of external objects. Indeed, this is the basis for the several of the objections supporting monopsychism. In particular, the third objection observes that if there are distinct human intellects, then the intelligible species of an object received in different intellects will themselves be individuals. But what is received in the intellect is a universal; so this appears to be a contradiction. The fourth objection takes this further: these individual intelligible species in the intellects of two separate individuals will have to undergo some process of abstraction in order to arrive as what is common to the two. But this seems to make the intellect of an individual something that is akin to the imagination; that is, something from which abstraction takes place. Again, this seems to be a contradiction, in this case to the nature of the intellect itself. Finally, the fifth objection observes that the understanding in the mind of a student is the same thing as is in the mind of the teacher; if it is numerically equal, then it must be present in something shared by them.

The first objection returns to the question left dangling at the end of the previous question: as we saw in the case of the angels, immaterial substances are not individuated by matter; therefore if they are to differ from one another, they must differ in species.

Aquinas’s response is thoroughly uncompromising: “it is altogether impossible for there to be a single intellect for all men”, “it is altogether impossible and absurd to posit a single intellect for all men”. Clearly this was an important issue, as he takes the trouble to provide a number of answers. The first answer assumes Platonism, the second an Aristotelian framework and the third purports to make no assumptions about how the soul is united to the body!

From a Platonic point of view, identifying a man with his intellect, the answer is clear; the existence of only one intellect would imply that the distinction between two individuals would not be of their essences, an absurd position. Likewise looked at from the position of an Aristotelian, numerically diverse things cannot share in one form.

To attack the problem more generally, Aquinas considers how the intellects of this man may be united with the intellect of that man. They might be united as a single principle agent with two instruments; or as a two different principle agents with a single instrument; or as a single principle agent with a single instrument. Whichever way you look at it, the inevitable consequence is that if there is only a single intellect then there can only be a single knower. We end up with a situation where there can only be a single knower and a single act of understanding. We can be quite happy with the idea that there can be different phantasms of, say, a rock in our hypothetical single intellect and that these could be the phantasms of different people; but the form in the potential intellect is an intelligible species abstracted from the phantasms from which a single universal concept is abstracted. Each person would have the same single universal and there would only be a single act of understanding. This means that the act of understanding could not distinguish this man from that man.

In reply to the third and the fourth objection, Aquinas observes that it is not the individuality of an intellectual soul that would provide a barrier to understanding universals, but rather any materiality associated with the soul. It is the immateriality of the soul that allows for the complete abstraction from material conditions. He also points out that even if there were only one human soul in the universe, it would itself be an individual and the intelligible species through which it derived understanding would itself be an individual. Furthermore, what is understood in the intellect exists in the intellect as an image of the object of perception; however, what is understood by the human is the object of perception itself. It’s perfectly possible for the same thing to be known by different knowers, as what they know is the same thing.

The trap left over from Ia.q75.a7 that is raised in the first objection is dealt with by observing that although the intellective soul has no matter in its make up to individuate it, it still is the form of a certain parcel of matter; it is this latter that serves to individuate it. Lest one should worry that this individuation goes away when the body dies, the reply to the second objection observes that the soul retains its own being (it is, after all, subsistent). It has existed as diverse from other souls; in retaining its being it remains diverse.

A3: We’ve seen that it is the intellective soul that makes a human being to be a human being; but are there separate forms that makes the human to be alive in the first place and then to be sentient? Are the three forms, the nutritive, the sensitive and the intellective “layered” on top of one another in the human being?

Once one has accepted that the human soul is the substantial form of the body, argues Aquinas, then this position really makes no sense. Things do only have one substantial form, the form that makes them to be what they are. In the first place, denying the unity of the substantial form would be to deny the unity of the thing itself; a collection of substantial forms would lead to a collection of beings rather than one unified whole. In the second place, the relationship between substantial forms would either have to be accidental or per se. If it were accidental then we would be saying either that an animal was accidentally a human or that a human was only accidentally an animal, neither of which makes any sense. If it were per se, then we would have to be looking for the definition of each one in the other; and one cannot find the definition of human in the definition of animal. Finally, the operations of the soul work as a unity, sentient and intellective, they do not impede each other as they might if they arose from two separate substantial forms.

The third objection raises the important issue of human development. In his answer, Aquinas acknowledges that in the development of the embryo it would seem that there is first a sentient soul that is later replaced by an intellective soul. He will return to this issue in more detail latter (Ia.q118.a2). In brief, the reasoning behind this lies in the fact that a form can only be received in matter that is fitted for the reception of that form. The science of the day suggested that the matter of the early embryo was not suitable for the reception of an intellective soul and hence ensoulment was thought to happen at some time after physical conception. In is interesting to speculate that Aquinas would probably be of a different opinion in the light of modern embryology.

In his reply to the fourth objection, Aquinas makes an important point about how we perceive and categorize the world. The substance of the objection is that when we think about the genus animal and the difference rational that characterizes humans there would seem to be a correspondence between matter that determines the genus and form that characterizes the difference. This suggests that a body animated by a sentient form should be considered as the “matter” that is informed by the soul. Aquinas answers that, in the world, there is no need for a real diversity corresponding to how we understand the world: “reason can apprehend one and the same entity in diverse ways”. The idea of a genus is one of our conceptual ways of organising our thinking about the world: we abstract the idea of the genus animal from our observations of the commonality between humans and other animals and arrive at the difference rational from the same observations. This genus/difference classification is how our mind thinks about the world, but it need not correspond exactly to the actual way that the world is put together.

A4: At first sight, the existence of this article may seem a puzzle; hasn’t Aquinas already answered the question of whether there are other substantial forms in man than the soul? Indeed the first objection appears to be a rehash of the fourth objection of the previous article. The point is that in the third article Aquinas was dealing with the specific idea of nutritive, sentient and intellective substantial forms as the formal structure of humans. Here, as the sed contra suggests, he is dealing with full generality: a being has a single substantial being; the substantial form of a being is what gives being to the being; the soul is the substantial form of the human; end of argument. The body of the article is really just a swift reiteration of what substantial and accidental forms are and how they differ; a revision exercise for those students who may have nodded off earlier in the course at a vital moment. A substantial form is what gives being absolutely to something; an accidental form gives being in-a-certain-sort-of-way to something. The intellective soul is the substantial form of man and the fact that a human being is also an animal and a living thing merely reflects that the nutritive and sentient elements of humans are subsumed under the intellective soul. Aquinas uses the (slightly misleading) terminology that the intellective soul virtually contains the nutritive and sentient souls. This doesn’t mean that the latter are actually present as forms in the intellective soul; rather, the intellective soul includes everything that would be contained in the nutritive and sentient souls.

The fourth objection gives Aquinas the opportunity to talk about mixtures: it would seem more reasonable to consider that the basic elements that make up the human body maintain their substantial existence, therefore each element in the body has its own substantial form and the body is really a mixture of these elements. Against Averroes and Avicenna, Aquinas argues that in a mixture there is not really something new created but rather that if one looks close enough one will see the individual elements in place. The substantial forms of these individual elements in the mixture do not remain actually in existence but exist virtually in the substantial form of the whole mixture. The substantial form of a whole “takes over” everything to do with the substantial forms of the parts that go to make up the whole.

A5: Given that the intellective soul is such a remarkable thing, it doesn’t really seem fitting that it is united with such a pathetic body. On the one hand the body is incorruptible whereas the soul is not, on the other hand the human body, compared to animal bodies, seems rather lacking in physical attributes.

Aquinas answers that because matter exists for the sake of form, rather than form for the sake of matter, the reason matter is the way it is entirely due to the form itself. The intellective human soul, on the bottom rung of intellective substances, has to possess the power of sensing as it does not have the sort of immediate access to knowledge that the higher intellective substances do. Therefore the soul has to be united to the sort of body that is suitable for this purpose. The human body, Aquinas claims, is the most balanced with regard to its sensory equipment amongst the animal kingdom. Would this claim stand up to modern scrutiny? The human body certainly does not have the most acute of senses in the animal kingdom, but Aquinas might respond that this is not the point: what matters is how they work together such that the common sense (the internal sense that integrates the input of the external senses) can make a better model of the world for the intellect to ponder upon than can other animals.

The reply to the fourth objection (that other animals have much better built in tools and defences) is interesting: the intellective soul is ordered towards the comprehension of everything, therefore giving it determinate natural defences or weaponry would be futile. What humans are equipped with is the means by which they can fashion what they need for their particular circumstances. The hands, for example, are the “instrument of instruments”.

A6: When a new thing comes into existence a new substantial form replaces the form(s) out of which the new thing is made. It’s a fundamental principle that the matter out of which a new thing is made must be suitable to the reception of the new substantial form. But surely this means that there must be a number of accidents present (such as size and shape) that make the matter suitable for the reception of the new substantial form and therefore the union of substantial form to matter (and therefore of intellective soul to body) must be mediated by some accidents? It seems that these accidents are prior to the substantial form in the new thing.

This confusion arises from failing to understand how certain things exist virtually in a substantial form. The matter out of which something new is made does have to have certain accidental properties that allow for the new substantial form to take its place. But these accidents are also contained virtually in the new substantial form, so that when the new substantial form is in place they are proper accidents contained virtually in the substantial form rather than being added to or mediating the substantial form. The substantial form takes over, as it were, what was formally attributed to the accidents.

A7: The sixth article asked whether the union of the soul and the body is mediated by accidents. This article poses the further question: if not mediated by accidents, could the union be mediated by some body or bodies? The answer is straightforward, being simply a reiteration of what has gone before: the union of a substantial form with matter is not mediated by anything; to think so is simply to misunderstand how it all works.

That Aquinas makes the point about the union of a substantial form with matter over and over again shows that he was either dealing with some rather dense students, which is unlikely, or that the issue was a live one at his time. There were a number of opinions on the union of soul and body around at the time and much heat was generated in their discussion. Ultimately, Aquinas’s opinion won the day; mostly because it was difficult to fit the other theories into any sort of systematic metaphysics. Indeed these alternative ideas tended to last longest amongst those who were not particularly systematically minded!

A8: If one, by accident I hope, cuts an earthworm in two then often the two halves continue to thrive. This suggests that the form of the earthworm, its sentient soul, is not strongly localised to any part of the body. Is the same true of the intellective soul of the human? After all, cutting a human in two doesn’t usually end as well as it does for the earthworm.

The soul is the substantial form of the body; it is the thing that makes the being what it is. So, in particular, the soul must inform all parts of the body, making them to be what they are and making them to work together as a whole. So, the soul must be present in the whole of the body and in all its parts. What is less clear, perhaps, is whether the soul as a whole must be present in all parts of the body.

In order to answer this more specific question, Aquinas asks us to consider what we mean by wholeness and its relation to parts. He claims that there are three types of wholeness and related division into parts: one can divide a material object into quantitative parts; one can divide something into rational and essential parts, like the parts of a definition or the form and matter of a whole; one can divide a power into its virtual parts.

If we think about a patch of surface that is coloured white, then we observe that if the surface is broken up then each bit of surface will still be white; whiteness is both in the surface as a whole and in each of the parts individually. But this first quantitative type of wholeness in the parts only happens in certain circumstances where the whiteness is uniformly spread about the surface. For something like a soul that is informing different types of parts it simply cannot happen; there is a different relation to the whole and to the parts. On the other hand, the second and third types of wholeness can be applied to substantial forms. The soul does exist as a whole in each part of the body from the point of view of its essence but it does not exist in each part of the body with respect to its powers. For example, it is in the eye with respect to seeing and in the ear with respect to hearing but not vice versa. What is more, it does not exist in the whole body in the same way that it exists in the parts: it is primarily in the whole and secondarily in the parts insofar as they are ordered to the whole.

Handy Concepts

  • The definition of the Council of Vienne, that the soul is the form of the body, was reiterated as a definition of the faith in the eighth session of the fifth Lateran Council (1512-17). One might infer from this that there had been some resistance to the idea! One should note that the Lateran definition went further, confirming the teaching of the second article.
  • The fifth objection to the first article and its answer might be seen as a faint parallel to the question of whether there is one act of being in the hypostatic union of the God-man Jesus Christ.
  • The fifth objection to the second article should be dedicated to teachers the world over.
  • The seventh article makes mention of quintessence (or fifth essence). This was considered to be the form of matter that filled the universe above the terrestrial sphere. Funnily enough, the term has returned to modern physics attached to a hypothetical form of dark energy.


  • The process of intellection abstracts a universal of the object of cognition from the phantasms present in the imagination. For each individual this results in an individual act of understanding, that is, each individual has a universal present as the expressed species corresponding to the intelligible species. If the object of perception is the same for two individuals, in what way do they share the universal that they abstract from their phantasms? In what way are the universals of “rock” different in each individual?
  • The doctrine of the unity of substantial form (article 3) was highly contested during the Middle Ages. The doctrine was even condemned by two archbishops of Canterbury, Kilwardby and Peckham.
  • A strict materialist might argue that human animals are accidentally human (article 3).
  • At what point in the formation of a mixture (objection 4 to article 4) do the forms of the elements disappear and the form of the mixture appear?


Tuesday, 13 August 2013

Question 75 – The Essence of the Human Soul


Having considered God and then spiritual creatures, Aquinas now turns to the consideration of human beings. He is going to spend a lot of time considering humanity (the whole of the second part of the summa is about human beings) before turning to the God-man Jesus Christ in part three. For the moment, we will be looking at the so-called Treatise on Human Nature that stretches from question 75 to question 102 of the first part of the summa. In his introduction to question 75, Aquinas tells us that he will consider the nature of humanity first (in questions 75-89) and then the production of humans (in questions 90-102). In thinking about the nature of human beings, he will consider the nature of the soul (questions 75-76), the powers or capacities of the soul (questions 77-83) and the operations of the soul (questions 84-89).

It’s always important to try not to interpret Aquinas in terms that apply to later philosophical ideas; this is especially true in the field of philosophical psychology covered by this treatise. For example, although Aquinas identifies the soul as a subsistent form, he is not a substance dualist in the sense of Descartes. Aquinas believes that the soul is the form of the body and that although the soul is subsistent, one should not interpret the soul and the body as being substances with an independent existence. Likewise it’s important to note that Aquinas uses terms such as intellect, mind, imagination, appetite with precise meanings that slot into his particular psychology. One should not read into his thinking elements derived from modern use of similar terminology.

Why this Question Matters.

In this question, Aquinas is going to discuss the nature of the soul considered in itself, turning to the way in which the soul is united to the body in the next question. Aquinas is aiming for the position that, in living things, the soul is the form of the body. Moreover, in human beings, the intellective nature of the soul implies that it is immaterial, subsistent and incorruptible. However, as is so often the case in the summa, he is going to work up to that position incrementally. He first considers whether the soul is a material body and then turns to the difference between the souls of human beings and non-human animals. The former possess an intellective soul, whereas the latter do not. This has the extraordinary consequence that the human soul is subsistent and, in fact, is a subsistent form. As a consequence of this, the human soul is incorruptible. Even while describing the extraordinary nature of the human soul, he is careful to emphasize the bodily nature of the human being as well; the soul is not the human person, only the soul/body composite is that.

All this, of course, tallies well with Christian doctrine concerning the soul; but Aquinas’s approach here is philosophical and not directly theological, firmly based on the teaching of Aristotle’s de anima.

The Thread of the Argument

A1: Aquinas starts his enquiry into the nature of the soul by asking whether the soul is a body. If we think in terms of the modern philosophy of mind, what he is considering here is part of the argument of whether the soul has a material explanation; can we, even if only in principle, reduce the explanation of the soul to an explanation of the behaviours of some material substances? In particular for this question, can we identify the soul itself with some material body? In order to answer this question Aquinas is careful to give a definition of the soul: it is “the first principle of life in those things around us that are alive”. In other words, a soul is the type of thing that explains the difference between something that is animated and something that is inanimate. It’s worth noting that Aquinas is using the term principle as a very general description of that part of a subject which explains something about the subject. He is looking for something about the subject itself which explains its mode of being.

In answer to those who would argue that the soul is a material body, Aquinas’ argument is disarmingly simple. We can see that living things can do certain things that non-living things cannot; we call these vital operations. It is clear that some vital operations at least can have principles that are material: a principle of seeing is the eye, for example. But what Aquinas is concerned with here is the first principle of these vital operations; being such a first principle of life or being alive cannot belong to a body simply by reason of it being a body. If the latter were the case, then every body would be a soul or every body would be alive. Therefore, there must be something added to a material body that is alive that makes it to be alive; it is a body of a certain sort and the soul is what distinguishes it from inanimate bodies.

The second objection raises a subject that is going to be important in the sequel, that of cognition. The objection itself doesn’t seem to be all that coherent, but argues that the soul must be a body if it is to be able to have cognition of material objects. The objection appears to be coming from the point of view that in order to have cognition of material objects, some likeness of these objects must exist in actuality in some way in the body; like must be like in order for cognition to occur and therefore such likenesses must occur in the nature of the body. Aquinas argues that the cognition of something involves the body in passing from potentiality to actuality; the body is in potentiality to form a likeness of a material object. But this does not mean that the body need have the likeness of the material object in its nature, only that the potentiality to form such likenesses exists in its nature. In the sequel, Aquinas will say much more about how the body passes from potentiality to actuality in the process of cognition.

A2: Just as the first article of this question may disappoint for its limited scope, so this second article may take the breath away for its audacity. The human soul is subsistent; that is, it has some sort of existence apart from the body.

That the human soul continues in existence after the death of the body is, of course, a matter of divine revelation. But here, Aquinas is intent on arguing for part of this position on purely philosophical grounds. One immediately gets a sense of the direction of Aquinas’s argument from the first line of his response; he identifies the human soul as being the principle of the intellectual operations in humans. These intellectual operations allow us to operate on our perceptions of material objects in order to have cognition of their natures. What is more, we can have cognition of all material natures. Aquinas then argues that since this is the case, a human intellect cannot have within itself the nature of any particular material body, because such a presence would inhibit the cognition of that particular material nature. Likewise, intellectual understanding is not gained through a bodily organ, since the determinate nature of that organ would prevent us having cognition of the nature of that organ. (N.B. Aquinas does not argue that bodily organs are not involved in the total process by which we arrive at an intellectual understanding of a material nature; simply that they cannot be involved in the final intellectual cognition of such a nature.)

This means that the mind or intellect has operations (the intellectual operations) of its own that do not involve a material body. But in order to have its own operations it must be subsistent, as only those things that are actual can have operations. Therefore the intellect is both immaterial and subsistent.

The replies to the objections contain some important principles. The common teaching of the time was that the soul is the form of the body; therefore it seems to make no sense to speak of the soul as being subsistent, a this-something (hoc aliquid) since it is the form-matter composite that is the this-something, not the soul on its own. Aquinas answers that we can think of something like a hand as a subsistent thing, a this-something, that is a part of something that is a complete subsistent thing. The human soul is subsistent in the sense that the hand is subsistent as a distinguishable part of some greater whole; but it is not subsistent in the sense of being complete in itself. Likewise, when we think of how the operations of a part of the body (such the eye seeing) relate to the operations of the whole we should think in terms of the whole operating by means of the operations of the parts. The human sees by means of the eye; the human understands by means of his soul.

A3: Aquinas has argued in the second article that the human soul is immaterial and subsistent. What about non-human animals; are their souls subsistent too? Aquinas takes it as foundational that what distinguishes the human being from the non-human animal is that the former is in possession of an intellect whereas the latter is not. Non-human animals are sentient (and therefore in possession of a sentient soul) but they are not intellective; they cannot extract and abstract the quiddity of things from their sensations of things.

Aquinas acknowledges that Plato considered non-human animals to have subsistent souls, on the basis that although intellective activity is distinguishable from sentient activity, they both arise from immaterial principles. Aristotle, against Plato, argued that only intellective understanding is incorporeal and that sentient activity is completely associated with bodily change. Aquinas aligns himself with this position, arguing that sentient activity arises entirely from the activity of the conjoined body and soul. The sentient soul has no activity in and of itself and therefore cannot be considered to be subsistent. Again, it is important to note that Aquinas is quite willing to admit that bodily change occurs as part of the complete process by which humans arrive at an intellectual understanding of some object; it is the final step of intellection that is entirely immaterial in human beings.

A4: If one is a substance dualist, there is a danger that one may believe the body to be only a sort of container for what is really me; my soul. Similarly, an overemphasised spirituality will tend to downplay the role of the body in the human person. Having shown that the human soul is subsistent, one might also think that Aquinas would lean this way. But he will have none of this; I am not my soul, I am the composite of soul and body.

Aquinas offers two arguments in support of this position. For the first he looks at how one would understand the definition of human. For all natural things, the definition refers to both the form and the matter. One might refer to the definition of human in general (in which case one sees that man comprises soul and flesh and bone) or to a human (in which case one sees that this human comprises this soul and this flesh and bone). Either way, body is irreducibly part of the definition of human. For the second argument, Aquinas turns to what has been argued in the third article; the sentient operations of an animal are irreducibly performed by the soul/body composite. This much applies to humans as much as it does to non-human animals. Therefore one cannot understand the operations of a human (and therefore the human himself) without the notion of the soul/body composite.

A5: Is it possible that the soul is itself composed of matter and form? Aquinas offers two arguments against this. In the first argument he comes out and states explicitly that the soul is the form of the body. If there were some part of the soul that was material then we could simply ignore that part and take the immaterial formal part as being the form of all the rest and call that the soul.

The second argument is perhaps more interesting in the sequel and refers in particular to the human soul rather than to souls in general. The human soul is intellective and as such has the cognition of the quiddity of things. In order to have this cognition of a thing (such as a rock), the form of that thing has to exist in some manner in the soul of the person having the cognition. What is more, the cognition of that rock is a cognition of the universal, the what-ness of it, abstracted away from the particular rock. Now, we recall that matter is the principle of the individuation of things (this rock is different from that rock because it is composed of a different lump of designated matter). If the intellective soul contained matter, then the forms it receives in cognition would inform the matter of the soul and we would only receive those forms as individuals. Therefore since we know that the intellective soul has cognition of universals, it must be immaterial.

Aquinas emphasizes this latter position in the reply to the first objection, which involves a rather intricate argument about the connection between the neo-Platonic idea of procession and the Aristotelian ideas of actuality and potentiality. The soul moves from potentiality to actuality in cognition and therefore it seems that it would have to participate in pure potentiality (that is, prime matter) in order to do this. But the intellective soul does not receive individual forms in the way that prime matter receives individual forms. Rather the intellect receives absolute forms (that is, universals) and these are not individuated in matter. The receptive potentialities of prime matter and of the intellective soul differ from one another in this mode of reception.

The fourth objection raises the possibility that we might have too elevated a notion of human soul. A subsistent, immaterial form begins to sound a bit too much like God himself. Fortunately Aquinas has already gone through this problem in the case of the angels (Ia.q50.a1); in parallel with that argument, one must look to the composition of actuality and potentiality as being more primary that the composition of matter and form.

A6: One of the consequences of the human soul being a subsistent form (article 2) is that it must be incorruptible. Once having been created, the only way that a human soul ceases to exist is for God to remove its participation in being; it does not naturally die or degenerate or decompose with the death of the body.

To show this, Aquinas first distinguishes between per se and per accidens generation and corruption. When one considers the components of something composite, where the components do not subsist on their own, such as accidents or the forms of material objects, they are generated and corrupted per accidens. That is, they come into being and go out of being because the composite itself has come into or gone out of being. On the other hand, things that subsist per se can only come into being and go out of being per se. Their generation and corruption do not depend on some composite apart from the composition of actuality and potentiality; in particular, they only go out of being if their actuality, their esse, is withdrawn.

As the human soul is a subsistent form, it can only be corrupted per se, in common with any subsistent form. But being belongs to a subsistent form by its very nature; so in the natural order of things, it cannot cease to exist. The only way that a subsistent form can cease to exist is if God withdraws esse from it.

Aquinas goes on to offer two more arguments in favour of the incorruptibility of the human soul. The first covers the situation where one might take a wider definition of the soul to include some composition of matter and form (as in article 5). In this case, Aquinas argues that in order to corrupt, some form of contrary is required (one might think of a pathogenic attack within the body as being such a contrary). But although the human soul is able to form concepts of contraries, contraries themselves do not exist within the soul. Finally, Aquinas offers the heuristic argument that the intellect apprehends being in an absolute sense and that consequent upon that apprehension is a natural desire for that being. On the principle that a natural desire cannot be in vain, this would imply that the desire for being is never naturally frustrated for the human soul.

The third objection to this article argues that nothing can exist without its proper operation and that the proper operation of the human soul is intellective understanding using phantasms. But after death, there are no phantasms and therefore there can be no intellectual operations. In his reply to this objection, Aquinas grants that intellectual understanding in conjunction with phantasms is proper to the soul as it is united with the body. But he argues that when separated from the body it will have another mode of intellective understanding. He leaves the question of what this latter mode of understanding might be for Ia.q89.a1.

A7: The fourth objection to the fifth article of this question has already raised the spectre that the human soul as subsistent form might be too elevated a notion. The day was saved there by pointing out that a subsistent form can still be a composition of actuality and potentiality rather than having to be pure actuality. But we now recall that angels are pure forms that are compositions of actuality and potentiality; so are human souls simply some sort of species of angel? They are, after all, very similar to one another in nature in many respects. The particular question that Aquinas asks under this theme is whether the human soul belongs in some species of angel.

In answer, Aquinas reiterates the argument of Ia.q50.a4 where he showed that each angel inhabits a species of its own. Angels are immaterial and since matter is the principle of individuation within species there cannot be more than one individual angel within a species. The same argument extends to show that the human soul cannot inhabit a species already inhabited by an angel, as the human soul and an angel are clearly different (they have different intellectual operations, for example). Aquinas even goes so far as to extend the argument to the case where the human soul is considered to have some matter in it (as in article 5).

Notice that Aquinas seems to have laid a trap for himself. Surely the reasoning of this article means that distinct human souls must inhabit distinct species? Aquinas will address this problem in Ia.q76.a2.

Handy Concepts

  • The Latin word that is translated in English as soul is anima. We can see the etymological connection to words such as animated and animal. The fundamental idea is that the soul is what distinguishes animate objects from inanimate objects.
  • The reply to the first objection of the second article amounts to Aquinas’s denial of substance dualism.
  • In this question, Aquinas uses a lot of terminology to which he doesn’t give strict definitions. He will go into much greater depth as he proceeds through this treatise and things should become clearer! For the moment, we’ll give some elementary introductions. Phantasms are introduced as things that the soul uses in its act of understanding. A phantasm is the image (composed of all sensory components) that the imagination calls to mind when thinking about an object. Similarly, Aquinas introduces the idea of the intellect which is that power of the soul that enables humans to have cognition of the what-ness (quiddity) of things. In the third article we see that Aquinas believes that non-human animals are sentient (in the sense of being able to sense things and to react to those sensations) but do not possess intellect; they are unable to abstract the what-ness of things from their sensations in the way that humans can. From a phantasm, the active part of the intellect (the active or agent intellect) extracts the quiddity of the object of perception. What results from this process of extraction is an intelligible species that is impressed upon the passive part of the intellect (the passive or possible intellect). From such an intelligible species, the intellect forms a concept of the object of perception.
  • Not long after Aquinas died, the ecumenical Council of Vienne (1311-12) defined as a doctrine of the faith that the human soul is the form of the body. “…we reject as erroneous and contrary to the truth of the catholic faith every doctrine or proposition rashly asserting that the substance of the rational or intellectual soul is not of itself or essentially the form of the human body, or casting doubt on this matter”. (Decrees of the Ecumenical Councils, Vol 1, tr. Tanner, p 361. See also DS902).
  • As non-human animals do not possess subsistent souls, they do not accompany us to heaven (or hell).
  • In thinking about the fourth article, we might call to mind that Aquinas wrote, rather poetically, in his commentary on 1 Corinthians 15 (lecture 2, para. 924) “…but the soul, since it is part of man’s body, is not an entire man, and my soul is not I”.
  • The idea that the soul itself might be a composition of form and some type of matter (article 5) is associated with Ibn Gebirol (Avicebron, 1021-70). The idea gathered some momentum in the Franciscan school after Aquinas’s death.
  • Aquinas wrote much about human psychology in Book 2 of the summa contra gentiles; in many ways this material is more systematically arranged than that of the summa theologiae. In addition, he wrote a commentary on Aristotle’s de anima and there is a collection of Aquinas’s disputed questions de anima.
  • By the end of this question we know that the human soul is an immaterial, subsistent and incorruptible form; the intellective nature of the human soul is what differentiates it from the non-human animals.


  • As we have seen, Aquinas takes for granted quite a lot of terminology to do with the way that the human soul works, even as he is explaining it. We will provide some background in each question sufficient to understand the question and will provide a summary of how everything fits together once we have reached the end of the treatise. For the time being, a useful but compact reference for understanding Aquinas’s approach to the human soul is Chapter 4 of Wallace’s The Elements of Philosophy. A useful reference for placing Aquinas’s approach to human psychology in a wider context is Maslin’s An Introduction to the Philosophy of Mind. One may, of course, also wish to dive into Aristotle’s de anima!
  • In the first article, Aquinas’s argument that the soul is not a body appears to amount to nothing more than an emphasis of his definition; the soul is that which differentiates between living and non-living things. Aquinas takes it as self-evident that there is a fundamental qualitative difference between things that are alive and things which are not. It’s important to note that Aquinas’s ambitions in this article are very limited; he is not arguing for the immateriality of the soul (he will do that later). Rather, he is arguing that some material bodies possess vital operations and that such operations cannot be explained simply by the fact that a body is a body.
  • The line of reasoning that Aquinas takes in the second article may disappoint, given all the avenues that he could have taken (such as the argument from intentionality, the argument advanced in the fifth article, or the arguments presented in the second part of the summa contra gentiles) and even given that he could have bolstered the argument that he has used. Perhaps we are seeing a consequence of the order that Aquinas has chosen to present the material on human nature; in order to present a more convincing argument he would have had to develop more sophisticated preliminaries; perhaps he felt this not suitable to the grade of student he was writing for!