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.

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