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.
- 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.