was not distrusting his eyes. But all these
instances are cited in order to prove that than which nothing can be more
certain, namely, that between true and false perceptions there is no
difference at all, as far as the assent of the mind is concerned. But you
prove nothing when you merely refute those false perceptions of men who
are mad or dreaming, by their own recollection. For the question is not
what sort of recollection those people usually have who have awakened, or
those who have recovered from madness, but what sort of perception madmen
or dreamers had at the moment when they were under the influence of their
madness or their dream. However, we will say no more about the senses.

What is there that can be perceived by reason? You say that Dialectics
have been discovered, and that that science is, as it were, an arbiter and
judge of what is true and false. Of what true and false?--and of true and
false on what subject? Will a dialectician be able to judge, in geometry,
what is true and false, or in literature, or in music? He knows nothing
about those things. In philosophy, then? What is it to him how large the
sun is? or what means has he which may enable him to judge what the chief
good is? What then will he judge of? Of what combination or disjunction of
ideas is accurate,--of what is an ambiguous expression,--of what follows
from each fact, or what is inconsistent with it? If the science of
dialectics judges of these things, or things like them, it is judging of
itself. But it professed more. For to judge of these matters is not
sufficient for the resolving of the other numerous and important questions
which arise in philosophy. But, since you place so much importance in that
art, I would have you to consider whether it was not invented for the
express purpose of being used against you. For, at its first opening, it
gives an ingenious account of the elements of speaking, and of the manner
in which one may come to an understanding of ambiguous expressions, and of
the principles of reasoning: then, after a few more things, it comes to
the sorites, a very slippery and hazardous topic, and a class of argument
which you yourself pronounced to be a vicious one.

XXIX. What then, you will say; are we to be blamed for that viciousness?
The nature of things has not given us any knowledge of ends, so as to
enable us, in any subject whatever, to say how far we can go. Nor is this
the case only in respect of the heap of