Heraclitus, one might suppose, would study memory carefully, but in the fragments of his philosophy that have come down to us nothing is said upon the subject.
In Plato we find a more modern psychology. According to him the thinking power of the mind, the understanding, is above the mere power of sense perceptions. It is this power which compares and considers, notes similarities and contrasts, unity and plurality, and forms ideas of relation between Being and Non-Being as well as relations of number and proportions. Among the elements of this power, recollection (ἀνάμνησις) is of prime importance. This rests upon the association by similarity and simultaneity.[[4]]
Plato distinguishes the passive retention (μνήμη) of perceptions from active memory (ἀνάμνησις),[[5]] and suggests as a definition of memory, “the power which the soul has of recovering, when by itself, some feeling which it experienced when in company with the body.” He attempts no explanation of memory of memory; but in the Theaetetus puts the following words into the mouth of Socrates:
“I would have you imagine, then, that there exists in the mind of man a block of wax, which is of different sizes in different men; harder, moister, and having more or less of purity in one than in another, and in some of an intermediate quality.... Let us say that this tablet is a gift of Memory, the mother of the Muses, and that when we wish to remember anything which we have seen or heard, or thought in our own minds, we hold the wax to the perceptions and thoughts, and in that receive the impressions from them as from the seal of a ring; and that we remember and know what is imprinted as long as the image lasts; but when the image is effaced, or cannot be taken, then we forget and do not know.”
Plato carries out the same figure to explain different degrees of memory. “When the wax in one’s soul is deep, abundant, smooth, and of the right quality, the impressions are lasting. Such minds can easily retain and are not liable to confusion. But, on the other hand, when the wax is very soft, one learns easily and forgets as easily; if the wax is hard, the reverse is true; again, if the wax is hard or impure, the impressions are indistinct; and still more indistinct are they when jostled together in a little soul.”[[6]]
This illustration must not be taken too seriously; for later on in the same dialogue Socrates calls it a “waxen figment” and substitutes for it the figure of the aviary of all kinds of birds—“some flocking together apart from the rest, others in small groups, others solitary, flying anywhere and everywhere.”
The receptacle is empty when we are young. The birds are kinds of knowledge. Learning is the process of capturing the birds and of detaining them in this enclosure. In acts of memory we re-catch them and take them out of the aviary.
Plato’s views upon memory have a special interest on account of their connection with his metaphysical doctrines. Perception and recollection are the occasion of the minds turning away from the world of sense to the inner world of innate and universal ideas. These ideas we could never get from sense-perception. That gives us only the immediate and the individual. The ideas are of the essential and the universal. We could not conceive them if we did not already know them. Hence the power to know the universal in the individual proves a previous existence in which we had the intuitions of universal truths; and, accordingly, learning is but recollection.[[7]] The metaphysical aspects of memory, however, let us avoid as much as possible. They would soon lead far from a psychological study. But this doctrine of recollection lies at the heart of the Platonic philosophy, and it is necessary to note carefully the distinction between this and ordinary memory. The latter, as defined by Plato in the passage quoted above is the memory or recollection of what has been learned through the body, that is, through sense-perception, belongs to the world of appearances, and is liable to many errors. The former, on the other hand, is not concerned with things of sense. It is recollection of that higher world where we had an antenatal vision of intelligible realities. Its highest manifestation is the insight of the philosopher who sees the divine goodness, truth, and beauty.[[8]]
II.
The difference in philosophic method between Plato and Aristotle is well illustrated by their treatment of memory. What Plato says of memory is incidental to the discussion of such profound matters as the nature of the soul and the theory of knowledge. Memory, according to him, is one of the higher faculties and partakes of the eternal nature of the soul. Aristotle makes a special study of memory in a less transcendental way. With him it is no longer a function of the eternal Nous; but it has its seat in the passive Reason, is dependent upon a physiological process, and perishes with the body.