of
themselves. For Epicurus, who wished to remedy those errors, which seem to
perplex one's knowledge of the truth, and who said that it was the duty of
a wise man to separate opinion from evident knowledge, did no good at all;
for he did not in the least remove the errors of opinion itself.

XV. Wherefore, as there are two causes which oppose what is manifest and
evident, it is necessary also to provide oneself with an equal number of
aids. For this is the first obstacle, that men do not sufficiently exert
and fix their minds upon those things which are evident, so as to be able
to understand how great the light is with which they are surrounded. The
second is, that some men, being deluded and deceived by fallacious and
captious interrogatories, when they cannot clear them up, abandon the
truth. It is right, therefore, for us to have those answers ready which
may be given in defence of the evidentness of a thing,--and we have already
spoken of them,--and to be armed, in order to be able to encounter the
questions of those people, and to scatter their captious objections to the
winds: and this is what I propose to do next.

I will, therefore, explain their arguments one by one; since even they
themselves are in the habit of speaking in a sufficiently lucid manner.

In the first place, they endeavour to show that many things can appear to
exist, which in reality have no existence; when minds are moved to no
purpose by things which do not exist, in the same manner as by things that
do. For when you say (say they) that some visions are sent by God, as
those, for instance, which are seen during sleep, and those also which are
revealed by oracles, and auspices, and the entrails of victims, (for they
say that the Stoics, against whom they are arguing, admit all these
things,) they ask how God can make those things probable which appear to
be false; and how it is that He cannot make those appear so which plainly
come as near as possible to truth? Or if He can likewise make those appear
probable, why He cannot make the others appear so too, which are only with
great difficulty distinguished from them? And if He can make these appear
so, then why He cannot also make those things appear so which are
absolutely different in no respect whatever?

In the next place, since the mind is moved by itself,--as those things
which we picture to ourselves in thought, and those which present
themselves to the sight of madmen or sleeping men