The New Academy.
The scepticism founded by Pyrrho soon became extinct, but an essentially similar doctrine began to be taught in the school of Plato. After the death of Plato, the Academy continued, under various leaders, to follow in the path marked out by the founder. But, under the leadership of Arcesilaus, scepticism was introduced into the school, and from that time, therefore, it is usually known as the New Academy, for though its historical continuity as a school was not broken, its essential character underwent change. What especially [{365}] characterized the New Academy was its fierce opposition to the Stoics, whom its members attacked as the chief dogmatists of the time. Dogmatism, for us, usually means making assertions without proper grounds. But since scepticism regards all assertions as equally ill-grounded, the holding of any positive opinion whatever is by it regarded as dogmatism. The Stoics were the most powerful, influential, and forceful of all those who at that time held any positive philosophical opinions. Hence they were singled out for attack by the New Academy as the greatest of dogmatists. Arcesilaus attacked especially their doctrine of the criterion of truth. The striking conviction which, according to the Stoics, accompanies truth, equally accompanies error. There is no criterion of truth, either in sense or in reason. "I am certain of nothing," said Arcesilaus; "I am not even certain that I am certain of nothing."
But the Academics did not draw from their scepticism, as Pyrrho had done, the full logical conclusion as regards action. Men, they thought, must act. And, although certainty and knowledge are impossible, probability is a sufficient guide for action.
Carneades is usually considered the greatest of the Academic Sceptics. Yet he added nothing essentially new to their conclusions. He appears, however, to have been a man of singularly acute and powerful mind, whose destructive criticism acted like a battering-ram not only upon Stoicism, but upon all established philosophies. As examples of his thoughts may be mentioned the two following. Firstly, nothing can ever be proved. For the conclusion must be proved by premises, which in turn require proof, and so ad infinitum. Secondly, [{366}] it is impossible to know whether our ideas of an object are true, i.e., whether they resemble the object, because we cannot compare our idea with the object itself. To do so would involve getting outside our own minds. We know nothing of the object except our idea of it, and therefore we cannot compare the original and the copy, since we can see only the copy.
Later Scepticism.
After a period of obliteration, Scepticism again revived in the Academy. Of this last phase of Greek scepticism, Aenesidemus, a contemporary of Cicero, is the earliest example, and later we have the well-known names of Simplicius and Sextus Empiricus. The distinctive character of later scepticism is its return to the position of Pyrrho. The New Academy, in its eagerness to overthrow the Stoic dogmatism, had fallen into a dogmatism of its own. If the Stoics dogmatically asserted, the Academics equally dogmatically denied. But wisdom lies neither in assertion nor denial, but in doubt. Hence the later Sceptics returned to the attitude of complete suspense of judgment. Moreover, the Academics had allowed the possibility of probable knowledge. And even this is now regarded as dogmatism. Aenesidemus was the author of the ten well-known arguments to show the impossibility of knowledge. They contain in reality, not ten, but only two or three distinct ideas, several being merely different expressions of the same line of reasoning. They are as follows. (1) The feelings and perceptions of all living beings differ. (2) Men have physical and mental differences, which make things appear different to them. (3) The different senses give different [{367}] impressions of things. (4) Our perceptions depend on our physical and intellectual conditions at the time of perception. (5) Things appear different in different positions, and at different distances. (6) Perception is never direct, but always through a medium. For example, we see things through the air. (7) Things appear different according to variations in their quantity, colour, motion, and temperature. (8) A thing impresses us differently when it is familiar and when it is unfamiliar. (9) All supposed knowledge is predication. All predicates give us only the relation of things to other things or to ourselves; they never tell us what the thing in itself is. (10) The opinions and customs of men are different in different countries.
TRANSITION TO NEO-PLATONISM
It has been doubted whether Neo-Platonism ought to be included in Greek philosophy at all, and Erdmann, in his "History of Philosophy," places it in the medieval division. For, firstly, an interval of no less than five centuries separates the foundation of Neo-Platonism from the foundation of the preceding Greek schools, the Stoic, the Epicurean, and the Sceptic. How long a period this is will be seen if we remember that the entire development of Greek thought from Thales to the Sceptics occupied only about three centuries. Plotinus, the real founder of Neo-Platonism, was born in 205 A.D., so that it is, as far as historical time is concerned, a product of the Christian era. Secondly, its character is largely un-Greek and un-European. The Greek elements are largely swamped by oriental mysticism. Its seat was not in Greece, but at Alexandria, which was not a Greek, but a cosmopolitan, city. Men of all races met here, and, in particular, it was here that East and West joined hands, and the fusion of thought which resulted was Neo-Platonism. But, on the other hand, it seems wrong to include the thought of Plotinus and his successors in medieval philosophy. The whole character of what is usually called medieval philosophy was determined by its growth upon a distinctively Christian soil. It was [{369}] Christian philosophy. It was the product of the new era which Christianity had substituted for paganism. Neo-Platonism, on the other hand, is not only unchristian, but even anti-christian. The only Christian influence to be detected in it is that of opposition. It is a survival of the pagan spirit in Christian times. In it the old pagan spirit struggles desperately against its younger antagonist, and finally succumbs. In it we see the last gasp and final expiry of the ancient culture of the Greeks. So far as it is not Asiatic in its elements, it draws its inspiration wholly from the philosophies of the past, from the thought and culture of Greece. On the whole, therefore, it is properly classified as the last school of Greek philosophy.