know
how that which contradicts itself can be comprehended, either
through itself or through something else, as no criterion of the
truth or of comprehension appears, and signs without proof would
be rejected, as we shall see in the next book. So much will
suffice for the present about suspension of judgment.

CHAPTER XVII.

_What are the Tropes for the overturning of Aetiology?_

In the same manner as we teach the Tropes of [Greek: epoche], 180
some set forth Tropes through which we oppose the Dogmatics,
by expressing doubt in regard to the aetiology of which they are
especially proud. So Aenesidemus teaches eight Tropes, by which
he thinks that he can prove all the dogmatic aetiology useless.
The first of these Tropes, he said, relates to the character 181
of aetiology in general, which does not give incontestable
testimony in regard to phenomena, because it treats of unseen
things. The second Trope states that although abundant resources
exist by which to investigate the cause of a thing in question,
some Dogmatics investigate it in one way only. The third Trope 182
states that the Dogmatics assign causes which do not show
any order for things which have taken place in an orderly
manner. The fourth Trope states that the Dogmatics, accepting
phenomena as they take place, think that they also understand
how unseen things take place, although perhaps the unseen things
have taken place in the same way as the phenomena, and perhaps
in some other way peculiar to themselves. The fifth Trope states 183
that they all, so to speak, assign causes according to their
own hypotheses about the elements, but not according to any
commonly accepted methods. The sixth states that they often
explain things investigated according to their own hypotheses,
but ignore opposing hypotheses which have equal probability. The
seventh states that they often give reasons for things that 184
not only conflict with phenomena, but also with their own
hypotheses. The eighth states that although that which seems
manifest, and that which is to be investigated, are often
equally inscrutable, they build up a theory from the one about
the other, although both are equally inscrutable. It is not
impossible, Aenesidemus said also, that some Dogmatics 185
should fail in their theories of causality from other
combinations of reasons deducible from the Tropes given above.
Perhaps also the five Tropes of [Greek: e