he Tropes of Agrippa were not in harmony. It was through
the very progress shown in the production of these Tropes that
the school finally lost the strength of its position.

Not content with having reduced the number of the Tropes from
ten to five, others tried to limit the number still further to
two.[2] Sextus gives us no hint of the authorship of the two
Tropes. Ritter attributes them to Menodotus and his followers,
and Zeller agrees with that opinion,[3] while Saisset thinks
that Agrippa was also the author of these,[4] which is a strange
theory to propound, as some of the material of the five is
repeated in the two, and the same man could certainly not appear
as an advocate of five, and at the same time of two Tropes.

[1] Saisset _Op. cit._ p. 237.

[2] _Hyp._ I. 178.

[3] Zeller III. 38; Ritter IV. 277.

[4] Saisset _Op. cit._ p. 231.

The two Tropes are founded on the principle that anything must
be known through itself or through something else. It cannot be
known through itself, because of the discord existing between
all things of the senses and intellect, nor can it be known
through something else, as then either the _regressus in
infinitum_ or the _circulus in probando_ follow.[1] Diogenes
Laertius does not refer to these two Tropes.

In regard to all these Tropes of the suspension of judgment,
Sextus has well remarked in his introduction to them, that they
are included in the eighth, or that of relation.[2]

[1] _Hyp._ I. 178-179.

[2] _Hyp._ I. 39.

_The Tropes of Aetiology_. The eight Tropes against causality
belong chronologically before the five Tropes of Agrippa, in the
history of the development of sceptical thought. They have a
much closer connection with the spirit of Scepticism than the
Tropes of Agrippa, including, as they do, the fundamental
thought of Pyrrhonism, _i.e._, that the phenomena do not reveal
the unknown.

The Sceptics did not deny the phenomena, but they denied that
the phenomena are signs capable of being interpreted, or of
revealing the reality of causes. It is impossible by a research
of the signs to find out the unknown, or the explanation of
things, as the Stoics and Epicureans claim. The theory of
Aenesidemus which lies at the foundation of his eight Tropes
against aetiology, is given to us by Photius as follows:[1]
"There are no visible signs of the unknown, and those who
believe in its existence are the victims of a vain illusion."