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Aristotle: Forms and Souls


Aristotle considered the most fundamental features of reality in the twelve books of the Μεταφυσικη (Metaphysics). Although experience of what happens is a key to all demonstrative knowledge, Aristotle supposed that the abstract study of "being qua being" must delve more deeply, in order to understand why things happen the way they do. A quick review of past attempts at achieving this goal reveals that earlier philosophers had created more difficult questions than they had answered: the Milesians over-emphasized material causes; Anaxagoras over-emphasized mind; and Plato got bogged down in the theory of forms. Aristotle intended to do better.

Although any disciplined study is promising because there is an ultimate truth to be discovered, the abstractness of metaphysical reasoning requires that we think about the processes we are employing even as we use them in search of that truth. As always, Aristotle assumed that the structure of language and logic naturally mirrors the way things really are. Thus, the major points of each book are made by carefully analyzing our linguistic practices as a guide to the ultimate nature of what is.

Fundamental Truths

It is reasonable to begin, therefore, with the simplest rules of logic, which embody the most fundamental principles applying to absolutely everything that is:

The Law of Non-Contradiction in logic merely notes that no assertion is both true and false, but applied to reality this simple rule entails that nothing can both "be . . . " and "not be . . . " at the same time, although we will of course want to find room to allow for things to change. Thus, neither strict Protagorean relativism nor Parmenidean immutability offer a correct account of the nature of reality. (Metaphysics IV 3-6)

The Law of Excluded Middle in logic states the necessity that either an assertion or its negation must be true, and this entails that there is no profound indeterminacy in the realm of reality. Although our knowledge of an assertion may sometimes fall short of what we need in order to decide whether it is true or false, we can be sure that either it or its negation is true. (Metaphysics IV 7-8)

In order to achieve its required abstract necessity, all of metaphysics must be constructed from similar principles. Aristotle believed this to be the case because metaphysics is concerned with a genuinely unique subject matter. While natural science deals with moveable, separable things and mathematics focusses upon immoveable, inseparable things, metaphysics (especially in its highest, most abstract varieties) has as its objects only things that are both immoveable and separable. Thus, what we learn in metaphysics is nothing less than the immutable eternal nature, or essence, of individual things.


In the central books of the Metaphysics, Aristotle tried to develop an adequate analysis of subject-predicate judgments. Since logic and language rely heavily upon the copulative use of "is," careful study of these uses should reveal the genuine relationship that holds between substances and their features. Of course, Plato had already offered an extended account of this relationship, emphasizing the reality of the abstract forms rather than their material substratum.

But Aristotle argued that the theory of forms is seriously flawed: it is not supported by good arguments; it requires a form for each thing; and it is too mathematical. Worst of all, on Aristotle's view, the theory of forms cannot adequately explain the occurrence of change. By identifying the thing with its essence, the theory cannot account for the generation of new substances. (Metaphysics VII) A more reasonable position must differentiate between matter and form and allow for a dynamic relation between the two.

Aristotle therefore maintained that each individual substance is a hylomorphic composite involving both matter and form together. Ordinary predication, then, involves paronymously attributing an abstract universal of a concrete individual, and our experience of this green thing is more significant than our apprehension of the form of greenness. This account, with its emphasis on the particularity of individual substances, provided Aristotle with a firm foundation in practical experience.

Higher Truths

Aristotle also offered a detailed account of the dynamic process of change. A potentiality {Gk. δυναμις [dynamis]} is either the passive capacity of a substance to be changed or (in the case of animate beings) its active capacity to produce change in other substances in determinate ways. An actuality {Gk. ενεργεια [energeia]} is just the realization of one of these potentialities, which is most significant when it includes not merely the movement but also its purpose. Becoming, then, is the process in which the potentiality present in one individual substance is actualized through the agency of something else which is already actual. (Metaphysics IX) Thus, for Aristotle, change of any kind requires the actual existence of something which causes the change.

The higher truths of what Aristotle called "theology" arise from an application of these notions to the more purely speculative study of being qua being. Since every being is a composite whose form and matter have been brought together by some cause, and since there cannot be infinitely many such causes, he concluded that everything that happens is ultimately attributable to a single universal cause, itself eternal and immutable. (Metaphysics XII 6) This self-caused "first mover," from which all else derives, must be regarded as a mind, whose actual thinking is its whole nature. The goodness of the entire universe, Aristotle supposed, resides in its teleological unity as the will of a single intelligent being.

The Nature of Souls

According to Aristotle, every animate being is a living thing which can move itself only because it has a soul. Animals and plants, along with human beings, are more like each other than any of them are like any inanimate object, since each of them has a soul. Thus, his great treatise on psychology, On The Soul, offers interconnected explanations for the functions and operations of all living organisms.

All such beings, on Aristotle's view, have a nutritive soul which initiates and guides their most basic functions, the absorption of food, growth, and reproduction of its kind. All animals (and perhaps some plants) also have a sensitive soul by means of which they perceive features of their surroundings and move in response to the stimuli this provides. Human beings also possess (in addition to the rest) a rational soul that permits representation and thought. (On the Soul II 2)

Notice that each living thing has just one soul, the actions of which exhibit some degree of nutritive, sensitive, and/or rational functioning. This soul is the formal, efficient, and final cause of the existence of the organism; only its material cause resides purely in the body. Thus, all of the operations of the organism are to be explained in terms of the functions of its soul.

Human Knowledge

Sensation is the passive capacity for the soul to be changed through the contact of the associated body with external objects. In each variety of sensation, the normal operations of the appropriate organ of sense result in the soul's becoming potentially what the object is in actuality. Thus, without any necessary exchange of matter, the soul takes on the form of the object: when I feel the point of a pin, its shape makes an impression on my finger, conveying this form to my sensitive soul (resulting in information). (On the Soul II 5)

Thought is the more active process of engaging in the manipulation of forms without any contact with external objects at all. Thus, thinking is potentially independent of the objects of thought, from which it abstracts the form alone. Even the imagination, according to Aristotle, involves the operation of the common sense without stimulation by the sensory organs of the body. Hence, although all knowledge must begin with information acquired through the senses, its results are achieved by rational means. Transcending the sensory preoccupation with particulars, the soul employs the formal methods of logic to cognize the relationships among abstract forms. (On the Soul III 4)

Desire is the origin of movement toward some goal. Every animate being, to some degree, is capable of responding to its own internal states and those of its external environment in such a way as to alleviate the felt absence or lack of some pleasure or the felt presence of some pain. Even actions taken as a result of intellectual deliberation, Aristotle supposed, produce motion only through the collateral evocation of a concrete desire. (On the Soul III 10)

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