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But even in the dogmatism of these early thinkers we can discern germs, which, when developed, were to give rise to Sophistry. All the philosophers after Parmenides and Heraclitus arrived at the opposition between knowledge and opinion, between rational and sensible knowledge. The operations of thought lead to results that are in evident contradiction with the testimony of our senses; and hence we must decide between the concrete data and the abstract products of thought. Heraclitus and Parmenides, Democritus, Empedocles, and Anaxagoras, agree in denying the veracity of our senses (see Vol. I., Chap. III. The Senses and External Perception). Now, by rational knowledge all these ancient philosophers understand, not a priori data, but the operations of thought upon the data of sense.
Was it not evidently a dangerous process for dogmatism to establish in this way a difference in value between rational and sensible knowledge, without distinguishing their origin? What right had they to allow to a knowledge that was derived, an authority they denied to primitive knowledge ?
And this was not the only side on which these systems laid themselves open to the attacks of the Sceptics. For Greek philosophy before Socrates was not only a dogmatism, but a physical dogmatism. Sensible knowledge was therefore not only the starting point of the whole of this philosophy, but the condition of its existence; and a philosophy that was led by its own results to dispute the worth of this knowledge destroyed the very principles on which it rested.
Besides this contradiction, which is inherent in all these systems, there was another which resulted from the disagreement between the systems themselves. Parmenides denies Becoming and the Many; Heraclitus sees in nature an infinite multiplicity, and a perpetual Becoming; Democritus attributes perpetual motion to his atoms; Anaxagoras finds it necessary to introduce an independent moving cause, namely, intelligence. The day had to come when the human mind, weary of these endless inquiries into the nature of things, would review the results arrived at by these researches. Then was suggested the oldest argument of Scepticism, namely, that from the contradictions among human opinions.
Thus it became an amusement to set the hypotheses of the different philosophers against one another. Contradictions were pointed out on every hand: between Parmenides and himself; between Parmenides and Heraclitus; between both of them and common sense. This clashing of contradictory ideas and arguments gave birth to Sophistry. The peculiarity of this form of scepticism is that it did not take the trouble to seek for any scientific basis. It did not invent its arguments, but borrowed them from former systems, and was content to develop them with a certain amount of skill. Some Sophists started from the doctrine of Heraclitus, others from that of the Eleatics, and from such opposite points of view they all arrived at the same conclusions.
Protagoras takes up the thesis of Heraclitus : everything is always in motion. It is only as objects move towards one another and mingle that they become something determinate; therefore it cannot be said that they are something, or even that they are at all, but only that they are becoming something. This theory applies as well to our knowledge. We are a variable term standing in an infinite number of relations to other objects. Things are to each man only what they appear to him to be, and they appear to him such as they must appear, given his peculiar state. “Man is the measure of all things, of those that exist and of those that do not exist." Upon such a principle no knowledge is possible; there is no escape from a chaos of contradictory opinions.
Gorgias adopts the argument of the Eleatics, but what they asserted only of multiple and changing being he applies to Being in general, and arrives at this threefold conclusion: 1st, there is nothing; 2nd, if there were anything we could not know it; 3rd, and if we could know it, we could not teach it to others (Sext. Emp. Adv. Math. VII, 77 sq.). This was more than Scepticism, it was absolute Nihilism.
Sophistry arose out of a dim consciousness of the law of contradiction. Though this principle was first formulated by Aristotle, the Sophists at least contributed towards its discovery, They had a notion of it as the criterion of truth, and in this way Sophistry was to a certain extent legitimate and fruitful. It showed the contradictions of the philosophers of the past, and it imposed on those of the future greater clearness and coherence in their systems, besides pointing out the necessity of commencing with a critical inquiry into the possibility of knowledge. So far, Sophistry had its raison d'être ; where it was wrong was in its hasty conclusions as to our radical incapacity to reach truth. It brought about its own destruction by violating the law of contradiction, in the name of which it had been founded. Sophistry went beyond doubt and negation even, and professed to maintain at the same time the most contradictory propositions. Thus it lost its hold on contemporary thought and provoked a reaction. In their dim conception of the law of contradiction lay the real strength of the Sophists, and it was by means of this law that Socrates brought about their ruin.
Socrates: Concepts the Objects of Knowledge; Subjective Certainty. Plato : Concepts and Ideas ; Objective Certainty.
While attacking the Sophists, Socrates in a certain sense carried on and completed their work. Philosophers deceive themselves, and we ourselves are deceived by our senses. From this the Sophists inferred that knowledge is impossible; but Socrates, on the other hand, infers only that it was impossible to reach science by the road hitherto taken, and he seeks a new method. Sensible knowledge by itself leads to contradictions, because it only shows us one aspect of things, the changing and fleeting surface. There is no science of the particular or accidental. Science has for its object the universal (Arist. Met. XIII, 1078 b, 17). It consists precisely in determining the concept, which reconciles apparent contradictions, and brings them to the unity of a single notion (Xenophon, Mem. IV, ii, 11). The object of the science of courage, for instance, is not a certain act of courage, but what is common to all courageous acts; it is one notion which is in the mind of all men when they use the word courage; it is the answer to the question, tí čomu ý årdpeia (Ibid. IV, vi, 15). Thus it is on concepts that Socrates re-establishes knowledge; these for him contain the principle of certainty. επί την υπόθεσιν επανήγε πάντα τον λόγον (Ibid. 13).
The criterion of certitude is that it puts an end to sophistical discussions, that it brings a man into harmony with himself and with others: οπότε δε αυτός τι τω λόγω διεξίοι διά των μάλιστα ομολογουμένων επορευέτο, νομίζων ταύτην ασφάλειας
“ Socrates also thought that those who knew the
nature of things severally would be able to explain them to others ” (Ibid.).
Socrates gives a reply to the arguments of the Sophists, but he does not attack the principles of scepticism; he asks himself how we can reach knowledge, but not if we can reach it. He does not question the possibility of arriving at certainty, but is only concerned in defining the manner in which it is to be sought. His philosophy implies a full belief in the possibility of knowledge, a belief which was both instinctive and profound, and which it did not occur to him to justify. With him, however, the conception we should form of knowledge becomes the first problem in philosophy. But his solution remained incomplete. Knowledge rests on concepts ; this is enough for subjective, but not for objective certainty. Are things in themselves such as our concepts represent them to be ? This postulate of which Socrates had not recognized the necessity was affirmed by Plato.
It is owing to Plato that certitude acquired an objective value. Our concepts exist outside ourselves. The true reality dwells in our objectified concepts, in notions, in the Ideas. Our concepts are, then, not only the principles of knowledge, but of existence itself. The ideal theory is a theory of certainty. To the question, how our concepts can be at once the types and images of reality, Plato replies by his theory of innate ideas. It is evidently not our concepts themselves, considered from the point of view of the individual, that determine reality. The Ideas, the principles of being, are not general ideas abstracted from the manifold phenomena (Phil. 16 c, Rep. 596 a), but they are discovered by an immediate intuition which is not the result of the mere elaboration of experience, but the ultimate term of a dialectic method (Rep. Bk. VII). The question remains, how does our soul originally obtain these concepts, which are at once the types and the images of reality ? To this question Plato answers by his theory of Reminiscence (Phaedrus, 246 sq.).
We must observe that the possibility of knowledge is not a subject of doubt to Plato any more than to Socrates. What he discusses is the conception that should be formed of true knowledge, never its possibility. The possibility of knowledge is in fact the principle on which the whole ideal theory depends. That knowledge is possible, and that true knowledge
is founded on concepts, was the postulate of Socrates, and Plato deduces its logical consequences. To say that concepts alone constitute true knowledge, or represent that which is, is to say that our concepts correspond to objective reality; in other words, what is intelligible exists, what is not intelligible does not exist, and reality is in direct proportion to intelligibility
Aristotle : Impossibility of Proving Everything; Intuitive Certainty of the Principles of Knowledge.
Aristotle does not, any more than his predecessors, question the possibility of knowledge. For him as for Plato knowledge deals with concepts, and is a certain knowledge of that which is general and universal το καθόλου. . So full was the confidence of these philosophers in the validity of thought, that Aristotle, who expressly attacks the Sceptics, does not even refer to the problem of certainty.
Science is the knowledge of the universal, and according to Aristotle the universal exists only through the particular. It is given to us in sensible reality (De Anima, III, viii, 432 a, 2), whence it must be abstracted ; and this is the function of induction. When once the universal is known, if our induction has not misled us, we should be able to deduce the particular from it. True knowledge is therefore demonstrative, and demonstration is the criterion of certainty. But will this criterion always be necessary? Demonstration is a syllogism starting from established premisses : will these premisses themselves always require to be proved ? To prove everything is impossible (Met. 1006 a, 9), for we should have to go on to infinity (εις άπειρον γαρ άν βάδιζον). The series of intermediate terms is not infinite, and where these intermediate terms end there appears an immediate knowledge, the knowledge of principles. These principles have the double characteristic of being incapable of proof and of not requiring proof (An. Post. II, 100b, 8). They are known with a greater certainty than anything that can be deduced from them.
They are the source of the certainty of which deduction is only the channel. The faculty by which they are known is reason (vous), and according to Aristotle this faculty never deceives us (De Anima, 429 a, 15-27; 430 a, 2).