Trust, not distrust, is the primitive attitude of the mind. What is put before us, whether by the senses or by the statements of others, is instinctively accepted as a veracious report, till experience has proved the possibility of deception. In the history of philosophy, in the same way, affirmation precedes negation; dogmatism goes before scepticism. And this must be so, because the dogmatic systems are, as it were, the food of scepticism; without them it would be without motive, without a basis operandi. Accordingly, we find that sceptical thought did not make its appearance till a succession of positive theories as to the nature of the real, by their mutual inconsistency, had suggested the possibility that they might all alike be false. The Sophistic epoch of Greek philosophy was, in great part, such a negative reaction against the luxuriance of self-confident assertion in the nature-philosophies of the preceding age. Though scepticism as a definite school of opinion may be said, in accordance with old precedent, to date only from the time of Pyrrho of Elis, there can be no doubt that the main currents of Sophistic thought were sceptical in the wider sense of that term. The Sophists were the first in Greece to dissolve knowledge into individual and momentary opinion (Protagoras), or dialectically to deny the possibility of knowledge (Gorgias). In these two examples we see how the weapons forged by the dogmatic philosophers to assist in the establishment of their own theses arc sceptically turned against philosophy in general. As every attempt to rationalize nature implies a certain process of criticism and interpretation to which the data of sense arc subjected, and in which they are, as it were, transcended, the antithesis of reason and sense is formulated early in the history of speculation. The opposition, being taken as absolute, implies the impeachment of the veracity of the senses in the interest of the rational truth proclaimed by the philosophers in question. Among the pre-Socratic nature-philosophers of Greece, Heraclitus and the Eleatics are the chief representatives of this polemic against the “lying witness” of the senses. The diametrical opposition of the grounds on which the veracity of the senses is impugned by the two philosophies (viz., by Heraclitus because they testify to an apparent permanence and identity in things, by the Eleatics because they testify to an apparent multiplicity and change) was in itself suggestive of sceptical reflexion. Moreover, although these philosophers are not in any sense themselves sceptical, their arguments are easily susceptible of a wider application. Accordingly we find that the arguments by which Heraclitus supported his theory of the universal flux are employed by Protagoras to undermine the possibility of objective truth, by dissolving all knowledge into the momentary sensation or persuasion of the individual. The idea of an objective flux, or law of change constituting the reality of things, is abandoned, and subjective points of sense alone remain,— which is tantamount to eliminating the real from human knowledge.

Still more unequivocal was the sceptical nihilism expressed by Gorgias in his three celebrated theses:—(1) nothing exists; (2) if anything existed, it would be unknowable; (3) if anything existed and were knowable, the knowledge of it could not be communicated. The arguments of his book, “Concerning the Non-existent, or Nature,” were drawn from the dialectic which the Eleatics had directed against the existence of the phenomenal world. Rut they are no longer used as indirect proofs of a universe of pure and unitary Being. The prominence given by most of the Sophists to rhetoric, their cultivation of a subjective readiness as the essential equipment for life, their substitution of persuasion for conviction, all mark the sceptical undertone of their teaching. This attitude of indifference to real knowledge passed in the younger and less reputable generation into a corroding moral scepticism which recognized no good but pleasure and no right but might.

What Socrates chiefly did was to recreate the instinct for truth and the belief in the possibility of its attainment. The scientific impulse thus communicated was sufficient to drive scepticism into the background during the great age of Greek philosophy (i.e. , the hundred years preceding Aristotle’s death, 323 B.C.). The captious logic of the Megaric school,—in which the Eleatic influence was strong,—their devotion to eristic and the elaboration of fallacies, was indeed in some cases closely related to sceptical results. The school has been considered with some truth to form a connecting link with the later scepticism, just as the contemporary Cynicism and Cyrenaicism may be held to be imperfect preludes to Stoicism and Epicureanism. The extreme nominalism of some of the

Cynics also, who denied the possibility of any but identical judgments, must be similarly regarded as a solvent of knowledge. But with these insignificant exceptions it holds true that, after the sceptical wave marked by the Sophists, scepticism does not reappear till after the exhaustion of the Socratic impulse in Aristotle.

The first man in antiquity whose scepticism gave name to his doctrine was Pyrrho of Elis (about 360-270 B. C. ). Pyrrho proceeded with the army of Alexander the Great as far as India, in the company of Anaxarchus, the Democritean philosopher. He afterwards returned to his native city, where he lived in poor circumstances, but highly honoured by his fellow-citizens. Pyrrho himself left no writings, and the accounts of his doctrine arc mainly derived from his pupil Timon of Phlius (about 325-235 B. c. ). Timon is called the Sillographist, from his satirical poem (Σtλλoι), in which all the philosophers of Greece are held up to ridicule, with the exception of Xenophanes, who honestly sought, and Pyrrho, who succeeded in finding, the truth. Other disciples are mentioned besides Timon, but the school was short-lived, its place being presently taken by the more moderate and cultured doubt of the New Academy. Zeller sums up Pyrrho’s teaching in three propositions: —We know nothing about the nature of things; hence tho right attitude towards them is to withhold judgment; the necessary result of withholding judgment is imperturbability. The technical language of the school expresses the first position by the word ακαταληψία ; things are wholly incomprehensible or inaccessible; against every statement the opposite may be advanced with equal justice (ίσoσθeveιa των λόγων). The sceptical watchword which embodies the second position is ϵ πoχη, reserve of judgment, or, as it is put by Timon, ov8ev μάλλον, that is, no one assertion is truer than another. This complete suspense of opinion is also expressed by the terms appcψia, or equilibrium, and aψaσιa, or refusal to speak, as well as by other expressions. The Pyrrhonists were consistent enough to extend their doubt even to their own principle of doubt. They thus attempted to make their scepticism universal, and to escape the reproach of basing it upon a fresh dogmatism. Mental imperturbability (αταραξία) was the result to be attained by cultivating such a frame of mind. Tho happiness or satisfaction of the individual was the end which dominated this scepticism as well as the contemporary systems of Stoicism and Epicureanism, and all three philosophies place it in tranquillity or self-centred indifference. Scepticism withdraws the individual completely into himself from a world of which he can know nothing. It is men’s opinions or unwarranted judgments about things, say the sceptics, which betray them into desire, and painful effort, and disappointment. From all this a man is delivered who abstains from judging one state to be preferable to another. But, as complete inactivity would have been synonymous with death, it appears to have been admitted that the sceptic, while retaining his consciousness of the complete uncertainty enveloping every step, might follow custom in the ordinary affairs of life.

The scepticism of the New Academy (or, to speak more strictly, of the Middle Academy, under Arcesilaus and Carneades, founders respectively of the so-called second and third Academies) differed very little from that of the Pyrrhonists. The differences asserted by later writers are not borne out on investigation. But the attitude maintained by the Academics was chiefly that of a negative criticism of the views of others, in particular of the somewhat crude and imperious dogmatism of the Stoics. They also, in the absence of certainty, allowed a large scope to probability as a motive to action, and defended their doctrine on this point with greater care and skill. The whole position was stated with more urbanity and culture, 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 intellectual, and they had something of the old delight in mental exercitation for its own sake. Arcesilas or Arcesilaus (about 315-240 b.c.) made the Stoic theory of irresistible impressions (ϕαvτασίαι κaτaληπτικaί) the special object of his attack. Mere irresistibleness (κατάληψις ), 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 (ΤΟ eυλoγov) 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 disposal. The theory of Carneades (213-129 b.c.) represents 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 ϵμϕασις and πιθανότης. 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 recognized 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 (πιθανη); in the second, probable and undisputed (πιθavη καί απερίσπαστος) ; in the third, probable, undisputed, and tested (πiθavη καϊ απερίσπαστος καϊ περιωδενμενη). 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 the third sceptical school—claimed to be a continuation of the earlier Pyrrhonism. Aenesidemus, though not absolutely the first to renew this doctrine, is the first of whose doctrine anything is known. He appears to have taught in Alexandria about the beginning of the Christian era. Among the successors of Aenesidemus, the chief names are those of Agrippa, whose dates cannot be determined, and the physician Sextus Empiricus (about 200 a.d.), whose Pyrrhonic Hypotyposes, and his work Adversus Mathematicos, 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 Aenesidemus belongs the first enumeration of the ten so-called tropes (τρόποι), or modes of sceptical argument, though the arguments themselves were, of 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 eliminated; the seventh refers to the changes which the supposed object undergoes in quantity, temperature, colour, motion, &c.; the eighth really sums up the thought which underlies the whole series, when it argues from the relativity of all our perceptions and notions; the ninth points out the dependence of our impressions on 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. Aenesidemus likewise attacked the notion of cause at considerable length, but neither in his arguments nor in the numerous objections brought against the notion by Sextus Empiricus do we meet with the thought which furnished the nerve of modern scepticism in Hume. The practical result of his scepticism Aenesidemus sought, like the Pyrrhonists, in αταραξία. He is somewhat strangely said to have combined his scepticism with a revival of the philosophy of Heraclitus; but the assertion perhaps rests, as Zeller contends, on a confusion. To Agrippa is attributed the reduction of the sceptical tropes to five. Of these, the first is based on the discrepancy of human opinions; the second on the fact that every proof itself requires to be proved, which implies a regressus in infinitum; the third on the relativity of our knowledge, which varies according to the constitution of the percipient and the circumstances in which he perceives. The fourth is really a completion of the second, and forbids the assumption of unproven propositions as the premises of an argument. It is aimed at the dogmatists, who, in order to avoid the regressus in infinitum, set out from some principle illegitimately assumed. The fifth seeks to show that reasoning is essentially of the nature of a circulus in probando, inasmuch as the principle adduced in proof requires itself to be supported by that which it is called in to prove. The attack made in several of these five tropes upon the possibility of demonstration marks this enumeration as distinctly superior to the first, which consists in the main of arguments derived from the fallibility of the senses. The new point of view is maintained in the two tropes which were the result of a further attempt at generalization. Nothing is self-evident, says the first of these tropes, for, if all things were certain of themselves, men would not differ as they do. Nor can anything be made certain by proof, says the second, because we must either arrive in the process at something self-evident, which is impossible, as has just been said, or we must involve ourselves in an endless regress.

When we review the history of ancient thought, we find, as Zeller puts it, that “the general result of all sceptical inquiries lies in the proposition that every assertion may be opposed by another, and every reason by reasons equally strong—in the ίσοσθϵveιa των λόγων. Or, as the same thing may be expressed, what all sceptical proofs come back to is the relativity of all our ideas. We can never know the nature of things as they are, but always only the manner in which they appear to us. The criterion of the sceptic is the appearance. Not even his own proof can claim truth and universal validity: he does not assert; he only seeks to relate how a thing strikes him at the present moment. And even when he expresses his doubts in the form of universal statements they are intended to be included in the general uncertainty of knowledge” (Phil. d. Griechen, iii. 2, p. 58). Both Zeller and Hegel, it may be added, remark upon the difference between the calm of ancient scepticism and the perturbed state of mind evinced by many modern sceptics. Universal doubt was the instrument which the sceptics of antiquity recommended for the attainment of complete peace of mind; rest and satisfaction can be attained, they say, in no other way. By the moderns, on the other hand, doubt is portrayed, for the most part, as a state of unrest and painful yearning. Even Hume, in various noteworthy passages of his Treatise, speaks of himself as recovering cheerfulness and mental tone only by forgetfulness of his own arguments. His state of universal doubt, so far from being painted as a desirable goal, is described by him as a “malady” or as “philosophical melancholy and delirium.” The difference might easily be interpreted either as a sign of sentimental weakness on the part of the moderns or as a proof of the limitation of the ancient sceptics which rendered them more easily satisfied in the absence of truth. It seems to prove, at all events, that the ancient sceptics were more thoroughly convinced than their modern successors of the reasonableness of their own attitude. But whether the ancients were the better or the worse...