St. Augustine developed the views of the Neo-Platonists in regard to memory. With him memory is a faculty of animals, men, and angels. God, whose immutable essence is above the sphere of movement and change, does not remember. Everything is seen by him in one indivisible and unchangeable present. Augustine does not agree with Aristotle that some animals are devoid of memory. He attributes memory even to fishes, and relates in confirmation of this opinion an incident that he had observed. There was a large fountain filled with fishes. People came daily to see them and often fed them. The fishes remembered what they received; and as soon as any one came to the fountain they crowded together expecting their accustomed food. But Augustine does not suppose that animals have that higher memory which is purely intellectual, although he probably failed to see how purely mechanical and involuntary their so-called acts of memory are. Memory with St. Augustine, as in the psychology of Plotinus, is a function of the soul, not of the body. But @with@ Aristotle @he@ refers it to the central sense.[34] What is memory? It is thinking of what one knows. All the various modifications of the soul cannot all be present to us at once. There is a difference between knowing a thing and thinking of it. The musician, says Augustine, knows music, but he does not think of it when he is talking about Geometry.[35] The ideas relating to music are in the mind in a latent state. Augustine anticipates Leibnitz in discussing the unconscious modifications of our ¬own¬ ideas; but he speaks especially of their gradual decay, while Leibnitz considers the unconscious growth of them. “Many numbers”,[36] Augustine says, “are gradually effaced from memory; for they remain not an instant unaltered. Indeed what is not found in memory after a year is somewhat diminished even after one day. But this diminution is imperceptible; yet it is not wrongly inferred; for it does not suddenly all vanish the day before the year is up. Hence we may conclude that from the moment it was engraved in memory it began to slip away.”[37] This doctrine of unconscious mental changes and unconscious mental states is one of the most remarkable features of Augustine’s psychology. With irresistible logic he demonstrates the existence of such states in the following passage from another place:—