ll outward reality, a point,
however, which they never quite reached.

[1] Pappenheim, _Die Tropen der Griechen_, p. 23.

[2] _Hyp._ I. 22.

[3] Diog. IX. 11, 61.

There is evidently much of Sextus' own thought mixed with the
illustrations of the Tropes, but it is impossible to separate
the original parts from the material that was the common
property of the Sceptical School. Many of these illustrations
show, however, perfect familiarity with the scientific and
medical teachings of the time. Before entering upon his
exposition of the Tropes, Sextus gives them in the short concise
form in which they must first have existed[1]--

(i) Based upon the variety of animals.

(ii) Based upon the differences between men.

(iii) Based upon differences in the constitution of
the sense organs.

(iv) Based upon circumstances.

(v) Based upon position, distance and place.

(vi) Based upon mixtures.

(vii) Based upon the quantities and constitutions
of objects.

(viii) Relation.

(ix) Based upon frequency or rarity of occurences.

(x) Based upon systems, customs and laws,
mythical beliefs, and dogmatic opinions.

[1] _Hyp._ I. 36-38.

Although Sextus is careful not to dogmatise regarding the
arrangement of the Tropes, yet there is in his classification of
them a regular gradation, from the arguments based upon
differences in animals to those in man, first considering the
latter in relation to the physical constitution, and then to
circumstances outside of us, and finally the treatment of
metaphysical and moral differences.

_The First Trope_.[1] That the same mental representations are
not found in different animals, may be inferred from their
differences in constitution resulting from their different
origins, and from the variety in their organs of sense. Sextus
takes up the five senses in order, giving illustrations to prove
the relative results of the mental representations in all of
them, as for example the subjectivity of color[2] and sound.[3]
All knowledge of objects through the senses is relative and not
absolute. Sextus does not, accordingly, confine the
impossibility of certain knowledge to the qualities that Locke
regards as secondary, but includes also the primary ones in this
statement.[4] The form and shape of objects as they appear to us
may be changed by pressure on the eyeball. Furthermore, the
character of reflections in mirrors depend