[253] Thus, for instance, the matter of instruction is either true or false; if false it would not be taught; for they assert that falsehood is non-existent, and of non-existents there could be no teaching. Nor yet if it were said to be true; for we have shown in our chapter ‟On the Criterion” ¹ that truth is non-existent. If, then, neither the false nor the true is being taught, and besides these there is nothing capable of being taught (for no one, to be sure, will say that, though these are unteachable, he teaches only dubious lessons ² ), then nothing is taught.

[254] And the matter taught is either apparent or non-evident. But if it is apparent, it will not require teaching; for things apparent appear to all alike. And if it is non-evident, then, since things non-evident are, as we have often shown, inapprehensible owing to the undecided controversy about them, it will be incapable of being taught; for how could anyone teach or learn what he does not apprehend? But if neither the apparent is taught nor the non-evident, nothing is taught.

[255] Again, what is taught is either corporeal or incorporeal, and each of these being either apparent or non-evident is incapable of being taught, according to the argument we have just now stated. Nothing, therefore, is taught.

[256] Further, either the existent is taught or the non- existent. Now the non-existent is not taught; for if the non-existent is taught the non-existent will be true, since teaching is held to be of things true. And if it is true, it will also subsist; for they declare that ‟a true thing is what subsists and is opposed to something.” ³ ‟But it is absurd to say that the non- existent subsists; therefore the non-existent is not taught.

[257] Yet neither is the existent. For if the existent is taught, it is taught either in so far as it is existent or in so far as it is something else. But if it is to be taught in so far as it is existent, it will be one of the existing things, and therefore a thing incapable of being taught; for teaching ought to proceed from certain acknowledged facts which require no teaching. ⁴ Therefore the existent, in so far as it is existent, is not capable of being taught.

[258] Nor, in fact, in so far as it is something else. For the existent has not anything else which is non-existent attached to it, so that if the existent in so far as it is existent is not taught, neither will it be taught in so far as it is something else; for whatsoever thing is attached to it is existent. And further, whether the existent thing which, they will say, is taught be apparent or non-evident, as it is subject to the absurdities we have stated, it will be incapable of being taught. But if neither the existent nor the non-existent is taught, there is nothing that is taught.