380 SCEPTICISM whole position was stated with more urbanity and cul- ture, and was supported, by Carneades in particular, by argumentation at once more copious and more acute. It seems also true that the Academics were less overborne than the Pyrrhonists by the practical issue of their doubts (imperturbability) ; their interest was more purely intel- lectual, and they had something of the old delight in mental exercitation for its own sake. Arcesilas or Arcesi- Arcesilaus (about 315-240 B.C.) made the Stoic theory of laus. irresistible impressions (<avTocnai /caToA^TrriKcu) the special object of his attack. Mere irresistibleness (Kcn-oA^ts), he maintained, is no criterion of truth, since false perceptions may equally possess this power to sway the mind. He seems chiefly to have supported his position by adducing the already well-known arguments of former philosophers against the veracity of the senses, and he evidently held that by these arguments the possibility of knowledge in general was sufficiently subverted. We can know nothing, he concluded, not even this itself, that we know nothing. He denied that the want of knowledge reduces us to inaction. Notions influence the will immediately, apart from the question of their truth, and, in all questions of conduct, probability (TO evXoyov) is our sufficient guide, as it is our highest attainable standard. It is stated that Arcesilaus made his negative criticism merely a preliminary to the inculcation of a modified Platonism. But this account, though not in itself incredible, is not borne out by any evidence at our Car- disposal. The theory of Carneades (213-129 B.C.) repre- neades. se nts the highest development of Academic scepticism. The dogmatic system which Carneades had in view was that of Chrysippus, the Stoic, whose main positions, whether in the theory of knowledge, in morals, or in theology, he subjected to an acute and thorough-going criticism. As to the criterion of truth, Carneades denied that this could be found in any impression, as such; for in order to prove its truth an impression must testify, not only to itself, but also to the objects causing it. We find, however, admittedly, that in many cases we are deceived by our impressions ; and, if this is so, there is no kind of impression which can be regarded as guaranteeing its own truth. According to his own examples, it is impossible to distinguish objects so much alike as is one egg to another ; at a certain distance the painted surface .seems raised, and a square tower seems round; an oar in water seems broken, and the neck-plumage of a pigeon assumes different colours in the sun ; objects on the shore seem moving as we pass by, and so forth. The same applies, he argued, to purely intellectual ideas. Many fallacies cannot be solved, and we cannot, for example, draw any absolute distinction between much and little, or, in short, between any quantitative differences. Our impressions, therefore, furnish us with no test of truth, and we can derive no aid from the operations of the understanding, which are purely formal, combining and separating ideas without giving any insight into their validity. Besides this general criticism of knowledge, Carneades attacked the cardinal doctrines of the Stoic school, their doctrine of God and their proof of divine providence from the evidences of design in the arrangements of the universe. Many of his arguments are preserved to us in Cicero's Academics and De Natura Deorum. His criticism of the contradictions involved in the Stoic idea of God really constitutes the first discussion in ancient times of the personality of God, and the difficulty of combining in one conception the characters of infinity and individuality. As a positive offset against his scepticism, Carneades elaborated more fully the Academic theory of probability, for which he employed the terms !/*<ao-is and iri6av6-nj<i. Being necessarily ignorant of the relation of ideas to the objects they represent, we are reduced to judging them by their relation to ourselves, i.e., by their greater or less clearness and appearance of truth. Though always falling short of knowledge, this appearance of truth may be strong enough to determine us to action. Carneades recog- nized three degrees of probability. The first or lowest is where our impression of the truthfulness of an idea is derived simply from the idea itself ; the second degree is where that impression is confirmed by the agreement of related ideas ; if a careful investigation of all the individual ideas bears out the same conclusion, we have the third and highest degree of probability. In the first case, an idea is called probable (Tridavr)) ; in the second, probable and undisputed (TnOav-rj KOL aTrepunracrTos) ; in the third, probable, undisputed, and tested (iriOavr] K<U aTrepicnraoTOS KOLL TrfpuaSevfj.emrj). The scepticism of Carneades was expounded by his successor Clitomachus, but the Academy was soon afterwards (in the so-called fourth and fifth Academies) invaded by the Eclecticism which about that time began to obliterate the distinctions of philosophical doctrine which had hitherto separated the schools. Cicero also, who in many respects was strongly attracted by the Academic scepticism, finally took refuge in a species of Eclecticism based upon a doctrine of innate ideas, and on the argument from the consensus gentium. The later scepticism which is sometimes spoken of as Later the third sceptical school ^claimed to be a continuation of scepti- the earlier Pyrrhonism. ^Enesidemus, though not abso- cis " 1 ' lutely the first to renew this doctrine, is the first of whose a " doctrine anything is known. He appears to . have taught in Alexandria about the beginning of the Christian era. Among the successors of ^Enesidemus, the chief names are those of Agrippa, whose dates cannot be determined, and the physician Sextus Empiricus (about 200 A.D.), whose Pyrrkonic ffypotyposes, and his work Adversus Matkematicos, constitute a vast armoury of the weapons of ancient scepticism. They are of the utmost value as an historical record. With Saturninus, the pupil of Sextus, and Favorinus, the grammarian, ancient scepticism may be said to disappear from history. What speculative power remained was turned entirely into Neoplatonic channels. To ^Enesidemus belongs the first enumeration of the ten so-called tropes (rpoTroi), or modes of sceptical Sceptioa argument, though the arguments themselves were, of tropes, course, current before his time. The first trope appeals to the different constitution of different animals as involving different modes of perception ; the second applies the same argument to the individual differences which are found among men ; the third insists on the way in which the senses contradict one another, and suggests that an endowment with more numerous senses would lead to a different report as to the nature of things; the fourth argues from the variability of our physical state and mental moods ; the fifth brings forward the diversities of appearance due to the position and distance of objects ; the sixth calls attention to the fact that we know nothing directly, but only through some medium, such as air or moisture, whose influence on the process cannot be elimi- nated ; the seventh refers to the changes which the sup- posed object undergoes in quantity, temperature, colour, motion, tfcc. ; the eighth really sums up the thought which underlies the whole series, when it argues from the rela- tivity of all our perceptions and notions ; the ninth points out the dependence of our impressions ou custom, the new and strange impressing us much more vividly than the customary ; the tenth adduces the diversity of customs, manners, laws, doctrines, and opinions among men. ^Enesidemus likewise attacked the notion of cause at con- siderable length, but neither in his arguments nor in the
