e same manner it is plain that there is another sort of proof
also which is distinct from assumption. For if in some sort of
argumentation it is sufficient to use assumption, and if it is not
requisite to add proof to the assumption; and if, again, in some sort
of argumentation assumption is invalid unless proof be added to it;
then proof is something separate and distinct from assumption. But
there is a kind of argumentation in which assumption does not require
proof; and a certain other kind in which it is of no use without
proof; as we shall show. Proof, then, is a thing distinct from
assumption. And we will demonstrate that which we have promised to in
this manner.

That assumption which contains a truth evident to all men has no need
of proof. That is an assumption of this sort:--"If it be desirable
to be wise, it is proper to pay attention to philosophy." This
proposition requires proof. For it is not self-evident. Nor is it
notorious to all men, because many think that philosophy is of no
service at all, and some think that it is even a disservice. A
self-evident assumption is such as this:--"But it is desirable to be
wise." And because this is of itself evident from the simple fact, and
is at once perceived to be true, there is no need that it be proved.
Wherefore, the argumentation may be at once terminated:--"Therefore
it is proper to pay attention to philosophy." There is, therefore, a
certain kind of assumption which does not stand in need of proof; for
it is evident that is a kind which does. Therefore, it is false that
argumentation is susceptible of only a threefold division.

XXXVII. And from these considerations that also is evident, that there
is a certain kind of argumentation in which neither proposition nor
assumption stands in need of proof, of this sort, that we may adduce
something undoubted and concise, for the sake of example. "If wisdom
is above all things to be desired, then folly is above all things to
be avoided; but wisdom is to be desired above all things, therefore
folly is above all things to be avoided." Here both the assumption and
the proposition are self-evident, on which account neither of them
stands in need of proof. And from all these facts it is manifest that
proof is at times added, and at times is not added. From which it
is palpable that proof is not contained in a proposition, nor in an
assumption, but that each being placed in its proper place, has its
own peculiar force