explanation of comets, that they are a collection of
vapors near the earth, because that coincided with his theory of
the universe.

VII. Theories of aetiology are presented which conflict not only
with individual hypotheses, but also with phenomena, as to admit
like Epicurus an inclination or desire of the soul, which was
incompatible with the necessity which he advocated.

VIII. The inscrutable is explained by things equally
inscrutable, as the rising of sap in plants is explained by the
attraction of a sponge for water, a fact contested by some.[2]

[1] _Hyp._ I. 98.

[2] _Hyp._ I. 180-186; Fabricius, Cap. XVII. 180 z.

Diogenes does not mention these Tropes in this form, but he
gives a _resume_ of the general arguments of the Sceptics
against aetiology,[1] which has less in common with the eight
Tropes of Aenesidemus, than with the presentation of the subject
by Sextus later,[2] when he multiplies his proofs exceedingly to
show [Greek: meden einai aition]. Although the Tropes of
Aenesidemus have a dialectic rather than an objective character,
it would not seem that he made the distinction, which is so
prominent with Sextus, between the signs [Greek: hypomnestika]
and [Greek: endeiktika],[3] especially as Diogenes sums up his
argument on the subject with the general assertion, [Greek:
Semeion ouk einai],[4] and proceeds to introduce the logical
consequence of the denial of aetiology. The summing up of the
Tropes of Aenesidemus is given as follows, in the _Hypotyposes_,
by Sextus:--"A cause in harmony with all the sects of
philosophy, and with Scepticism, and with phenomena, is perhaps
not possible, for the phenomena and the unknown altogether
disagree."[5]

It is interesting to remark in connection with the seventh of
these Tropes, that Aenesidemus asserts that causality has only a
subjective value, which from his materialistic standpoint was an
argument against its real existence, and the same argument is
used by Kant to prove that causality is a necessary condition of
thought.[6]

Chaignet characterises the Tropes of Aenesidemus as false and
sophistical,[7] but as Maccoll has well said, they are
remarkable for their judicious and strong criticism, and are
directed against the false method of observing facts through the
light of preconceived opinion.[8] They have, however, a stronger
critical side than sceptical, and show the positive tendency of
the thought of Aenesidemus.

[1] Diog. IX. 1