The Lives and Opinions of Eminent Philosophers Diogenes Laërtius (first ebook reader .TXT) 📖

These Skeptics then deny the existence of any demonstration, of any test of truth, of any signs, or causes, or motion, or learning, and of anything as intrinsically or naturally good or bad. For every demonstration, say they, depends either on things which demonstrate themselves, or on principles which are indemonstrable. If on things which demonstrate themselves, then these things themselves require demonstration, and so on ad infinitum. If on principles which are indemonstrable, then the very moment that either the sum total of these principles, or even one single one of them, is incorrectly urged, the whole demonstration falls instantly to pieces. But if anyone supposes, they add, that there are principles which require no demonstration, that man deceives himself strangely, not seeing that it is necessary for him in the first place to establish this point, that they contain their proof in themselves. For a man cannot prove that there are four elements because there are four elements.

Besides, if particular proofs are denied in a complex demonstration, it must follow that the whole demonstration is also incorrect. Again, if we are to know that an argument is really a demonstrative proof, we must have a test of truth; and in order to establish a test, we require a demonstrative proof; and these two things must be devoid of every kind of certainty, since they bear reciprocally the one on the other.

How then is anyone to arrive at certainty about obscure matters, if one is ignorant even how one ought to attempt to prove them? For what one is desirous to understand is not what the appearance of things is, but what their nature and essence is.

They show, too, that the dogmatic philosophers act with great simplicity; for that the conclusions which they draw from their hypothetical principles are not scientific truths but mere suppositions; and that, in the same manner, one might establish the most improbable propositions. They also say that those who pretend that one ought not to judge of things by the circumstances which surround them, or by their accessories, but that one ought to take their nature itself as one’s guide, do not perceive that, while they pretend to give the precise measure and definition of everything, if the objects present such and such an appearance, that depends solely on their position and relative arrangement. They conclude from thence, that it is necessary to say that everything is true, or that everything is false. For if certain things only are true, how is one to recognize them? Evidently it will not be the senses which judge in that case of the objects of sensation, for all appearances are equal to the senses; nor will it be the intellect, for the same reason. But besides these two faculties, there does not appear to be any other test or criterion at all. So, say they, if we desire to arrive at any certainty with respect to any object which comes under either sense or intellect, we must first establish those opinions which are laid down previously as bearing on those objects. For some people have denied this doctrine, and others have overturned that; it is therefore indispensable that they should be judged of either by the senses or by the intellect. And the authority of each of these faculties is contested; it is therefore impossible to form a positive judgment of the operations of the senses and of the intellect; and if the contest between the different opinions compels us to a neutrality, then the measure which appeared proper to apply to the appreciation of all those objects is at the same time put an end to, and one must fix a similar valuation on everything.

Perhaps our opponent will say, “Are then appearances trustworthy or deceitful?”136 We answer that if they are trustworthy, the other side has nothing to object to those to whom the contrary appearance presents itself. For, as he who says that such and such a thing appears to him is trustworthy, so also is he who says that the contrary appears to him. And if appearances are deceitful, then they do not deserve any confidence when they assert what appears to them to be true. We are not bound then to believe that a thing is true merely because it obtains assent. For all men do not yield to the same reasons; and even the same individual does not always see things in the same light. Persuasion often depends on external circumstances, on the authority of the speaker, on his ability, on the elegance of his language, on habit, or even on pleasure.

They also, by this train of reasoning, suppress the criterion of truth. Either the criterion has been decided on, or it has not. And if it has not, it does not deserve any confidence, and it cannot be of any use at all in aiding us to discern truth from falsehood. If, on the other hand, it has been decided on, it then enters into the class of particular things which require a criterion, and in that case to judge and to be judged amount to the same thing; the criterion which judges is itself judged of by something else, that again by a third criterion, and so on ad infinitum. Add to this, say they, the fact that people are not even agreed as to the nature of the criterion of truth: some say that man is the criterion, others that it is the senses which are so; one set places reason in the van, another class rely upon cataleptic perception.

As to man himself, he disagrees both with himself and with others, as the diversity of laws and customs proves. The senses are deceivers, and reason disagrees with itself. Cataleptic perception is judged of by the intellect, and the intellect changes in various manners; accordingly, we can never find any positive criterion, and in consequence, truth itself wholly eludes our search.

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