(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 entirely on their shape, as the images in concave mirrors are very different from those in convex ones; and so in the same way as the eyes of animals are of different shapes, and supplied with different fluids, the ideas of dogs, fishes, men and grasshoppers must be very different.[5]

    [1] Hyp..  I. 40-61.

    [2] Hyp..  I. 44-46.

    [3] Hyp..  I. 50.

    [4] Hyp..  I. 47.

    [5] Hyp..  I. 49.

In discussing the mental representations of animals of different grades of intelligence, Sextus shows a very good comprehension of the philogenetic development of the organs of sense, and draws the final conclusion that external objects are regarded differently by animals, according to their difference in constitution.[1] These differences in the ideas which different animals have of the same objects are demonstrated by their different tastes, as the things desired by some are fatal to others.[2] The practical illustrations given of this result show a familiarity with natural history, and cognizance of the tastes and habits of many animals,[3] but were probably few of them original with Sextus, unless perhaps in their application; that this train of reasoning was the common property of the Sceptic