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This theory of Aristotle is the best answer to a famous argument of the Sceptics—the impossibility of proving everything (An. Post. I, 3). But it pre-supposes precisely that which scepticism called in question, namely, the possibility of knowledge. If everything had to be proved, says Aristotle, knowledge would be impossible; what do I care, the Sceptic replies, it is precisely the possibility of knowledge that I dispute, and you answer me by starting from this assumption just as if it were a necessary principle. In fact, Aristotle's whole doctrine is inspired by the idea that certainty is and must be possible. He merely affirms the infallibility of our reason, and this is indeed all that can be done by those who wish to resist scepticism. If we are to find certainty, we must first of all believe in it.
Aristotle was not aware of the difficulty of his position, he was aware only of its strength, for he had that natural faith which is lacking in the sceptic. In order to defend the principle of contradiction, he shows that those who deny it condemn themselves to universal scepticism (Met. 1005 b, 11 sq.). To him, as to all strong minds, doubt is repugnant; he has faith in the veracity of his own faculties. He shows that scepticism is contradictory and refutes itself in practical life (Met. 1005 b, 25). He attacks it with all the scorn of one who is convinced of the soundness of his own reasons.
If his mind, he says of the sceptic, holds to nothing, if he at the same time believes and does not believe what he says, in what does such a man difer from a vegetable ? έστι δ' αποδείξαι ελεγκτικώς και περί τούτου ότι αδύνατον άν μόνον τι λέγη ο αμφισβητών.
ó αν δε μηθέν, γελοίον το ζητείν λόγον προς τον μηθενός έχοντα λόγον, ή μή έχει όμοιος γαρ φυτω ο τοιούτος ή τοιούτος ήδη. Finally, he says, like Spinoza, that the rôle of the sceptic is to be dumb: ου τω τοιούτω λόγος, ούτ' αυτω προς αυτόν, ούτε προς άλλον (Ibid.).
After Aristotle the Problem of Certainty is recognized. Stoicism : Subjective Criterion ; Tension of the Soul. Illogical Dogmatism of Epicurus.
After Aristotle the speculative interest was made subordinate to the practical. The human intellect, having grown feeble, began to doubt itself, and the possibility of knowledge appeared as a problem demanding solution. To discover an immutable rule of life and a sure measure of certainty and knowledge were the two questions with which henceforward philosophy was to concern itself (Ravaisson, Mét. d'Arist. Vol. II, p. 65).
But knowledge was only a means to happiness and Logic prepared the way for Ethics ; and thus the speculative postulate of Plato and Aristotle became a practical postulate. It remained to be seen whether the practical interest really did stand in need of a scientific conception. The Sceptics denied this, and there being no longer any justification or motive for it, science was declared to be impossible as well as useless.
Notwithstanding its dogmatic character, Stoicism already carried within it the germ of scepticism. It already discussed intellectual certainty, and, if it furnished a foundation for it, the foundation was too weak to resist the pressing attacks of the sceptics.
This weakness is a result of the gross materialism which was combined in the Stoic system with much that was noble and true.
For the Stoics nothing was real that was not a body, therefore nothing existed that could be known otherwise than by the senses. Sensible perception, however, was not purely passive : it followed the impression made by the object on the soul, and was distinguished from it. Knowledge begins with the consent we give to a representation when we refer it to an object (Sext. Emp. Adv. Math. VIII, 397). But what is it that determines this assent? In other words, by what signs do we recognize that a representation is a true one? There are representations which impose themselves on us with such force that we cannot refuse our assent to them, partagiai katalnetikai (D.L. VII, 46). These representations are in conformity with the reality and express the peculiar qualities (idiopata) which distinguish an object from all others (Sext. Emp. Adv. Math. VII, 250 sq.). For the Stoics maintain, as did Leibnitz later, that there are not two things in nature perfectly alike ; and from this they conclude " that there is, for everything, in every circumstance, one single representation which is infallible and truly comprehensive, and the sole object of the assent of the wise man” (Ravaisson, Métaph. d'Arist.). The real object is recognized by the impression, or shuck (pavracia evapyńs kaÌ TANKTIKń), which constitutes the evidence of its reality. But by what means do we measure the shock, the effect of the tension, which is the special quality perceived ? By the energy of the inner force, the tension of the perceiving soul. Thus we are brought back from the passivity of the soul on which the impression is made, to the peculiar activity by which it apprehends the object perceived. “Mens naturalem vim habet
. quam intendit ad ea quibus movetur” (Cic. Acad. II, 10).
Truth has its source in the force of the immediate conviction which the pavtadia kata nami” carries with it. This force belongs originally to internal and external perceptions, and also to the universal concepts, προλήψεις, κoιναι εννοίαι, which are unconsciously abstracted from them by the spontaneous activity of thought. In this way the Stoics could say that the criteria of the true are the φαντασία καταληπτική and the póanys (D.L. VII, 54). On the other hand the exactness of the methodically formed concepts has to be proved by scientific demonstration. Yet, when once they are proved, and this is an insoluble contradiction in the Stoic system,—they carry with them a certainty, not only equal but superior to the certainty of perceptions. If all reality is corporeal or individual, if every concept is only an abstraction, how could there be more truth in the thought of what is not real, than in the conception of the corporeal, which is reality itself? Yet Zeno compared a simple act of perception to the open hand, judgment to the closed hand, the concept to the fist, knowledge to the fist grasped by the other hand. The whole difference between these four forms of knowledge lies, as we see, in the greater or less force of the conviction. Certitude varies with the tension of the mind; there are in it differences of degree, but not of nature. In fact, the real criterion for the Stoics was neither the pavracia katałYTTiKÝ nor the mpónys, but the force of conviction, the tension of the mind, év Tóvự kai duvauet (Stob. Eclog. II, 128)—an entirely subjective criterion. The argument which recurs perpetually in their lengthy polemics against scepticism is the practical interest, the impotence of the man who doubts, the necessity of affirmation in practical life (Plut. De Stoic repugn. 47, 12: το μήτε πράττειν μήτε ορμαν
. , : ασυγκαταθετικός).
The Epicureans, like the Stoics, make the theory of knowledge subordinate to ethics. The sensualistic dogmatism of Epicurus rests on a practical postulate, on the need of a firmly established conviction in order to avoid the uncertainties of a life left to chance. Since his ethical system rests altogether on the sensations of pleasure and pain, sensation must be for him the criterion of truth.
“There were,” Epicurus said, “three criteria, the senses, the anticipations or primary notions, and the passions : κριτήρια της αληθείας είναι τας αισθήσεις και τας προλήψεις και τα πάθη” (D.L. X, 31). Through the passions we only know the pleasure and pain caused in us by things. They are the basis of practical philosophy. Anticipation, that by which we anticipate or divine sensation, is the impress (Tútos, D.L. x, 33) left by a. frequently repeated sensation. One may say then that, for Epicurus, in the last resort, the only criterion of truth and the principle of all speculative life was sensation. If you resist all the senses you will not even have anything left to which you can refer (D.L. X, 46). The only way of escaping from absolute doubt is to admit that sensation is always veracious.. Where we think to find errors of sense there are only errors of judgment. How can the testimony of sense be contradicted ? Is it by reason ? but rational knowledge is derived from sensible knowledge. Do our senses contradict one another? No; for each one of them has, in its own domain, an absolute validity. The different kinds of perceptions do not refer to the same thing (Sext. Emp. Adv. Math. VII, 203, sq.). Thus sensation itself is evidence (évápyela). Error is possible only when we go beyond sensation. Sensation is the criterion of the abstract concepts. which are valid only in so far as they are confirmed by sensation, and in some cases only in so far as they are not contradicted by it (D.L. x, 33).
Epicurus does not seem to have seen the difficulties inherent in this theory. All sensations as such are true; and this being the case, we must return to the argument of Protagoras. Epicurus tries to avoid this sceptical inference by his theory of the idola. Our senses are affected, not by the objects themselves, but by the images, the simulacra, which emanate from them. Now there are many of these images, and they may, moreover, become altered during the passage from the object to the sense which they affect. If, therefore, the same object appears different to different individuals it is not because the sensation is deceptive, but because the individuals have in reality perceived different objects, since they have been affected by different images.
But this is not a solution ; it merely puts the difficulty a step further back. How is the faithful image to be distinguished from the image that does not correspond to the object? We have outside us, as it were, two worlds which do not mingle though one is derived from the other—the world of images, the world of real objects. We only know the former through perception, and, as there is no constant relation between them, the latter remains unknowable. Thus science is deprived of all objective value; and the sensualistic subjectivity in which the theory of Epicurus culminates is not far removed from the scepticism of Pyrrho.
Pyrrho's Radical Scepticism. The new Academy: Criticism of the Stoic Dogmatism. Probabilism. Carneades: Theory of Degrees of Probability,
At this period of Greek philosophy everything seemed to conduce to scepticism. Even those who attacked it fostered it at the same time by their empiricism. They questioned the possibility of knowledge, and could find no better foundation for it than a practical postulate. If this postulate were overturned, if it were maintained that our practical interests do not depend upon knowledge, that, on the contrary, these interests would be better served by abandoning a knowledge that is, in any case, unattainable, then we should have a complete scepticism; and there would be nothing left to dogmatism wherewith to oppose it. It was the leading idea of Pyrrho to make the denial of knowledge the condition of the Sovereign Good.
Pyrrho lays down three propositions: 1st, that we can know nothing of the nature of things; 2nd, that we must consequently suspend our judgment concerning them ; 3rd, that the result of this suspension is atapačia, which is at once
, virtue and happiness.
We can know nothing of the nature of things, for how could we obtain certain knowledge ? Through our senses? Through them we know things, not as they are in themselves, but as they appear to us. Through reason ? But reason, even where it seems to have most authority, that is, in the moral sphere, rests on mere custom and habit (D.L. IX, 61). All we can do is to suspend our judgment ; ééYELV Tv συγκατάθεσιν ; a thing is not more this than that, ουδέν μάλλον (D.L. ix, 74). The doubt of the Sceptics does not refer to appearances, to phenomena (palvóueva), which are evident (evapyn), but to the reality which we are incapable of attaining (D.L. IX, 103). “But what is evidently seen prevails wherever it may be," says Timon (Ap. D.L. ix, 105). The moment we try to get beyond it we find ourselves confronted by contradictory and equipollent reasons which prevent all affirmation