[1] Diog. VII. 1, 86. [2] _Hyp._ I. 103. [3] _Hyp._ I. 104. [4] Diog. IX. 11, 82. [5] _Hyp._ I. 106. _The Fifth Trope_. This Trope leaves the discussion of the dependence of the ideas upon the physical nature, and takes up the influence of the environment upon them. It makes the difference in ideas depend upon the position, distance, and place of objects, thus taking apparently their real existence for granted. Things change their form and shape according to the distance from which they are observed, and the position in which they stand.[1] The same light or tone alters decidedly in different surroundings. Perspective in paintings depends on the angle at which the picture is suspended.[2] With Diogenes this Trope is the seventh,[3] and his exposition of it is similar, but as usual, shorter. Both Sextus and Diogenes give the illustration[4] of the neck of the dove differing in color in different degrees of inclination, an illustration used by Protagoras also to prove the relativity of perception by the senses. "The black neck of the dove in the shade appears black, but in the light sunny and purple."[5] Since, then, all phenomena are regarded in a certain place, and from a certain distance, and according to a certain position, each of which relations makes a great difference with the mental images, we shall be obliged also by this Trope to come to the reserving of the opinion.[6] [1] _Hyp._ I. 118. [2] _Hyp._ I. 120. [3] Diog. IX. 11, 85. [4] _Hyp._ I. 120; Diog. IX. 11, 86. [5] _Schol. zu Arist._ 60, 18, ed. Brandis; Pappen. _Er. Pyrr. Grundzuege_, p. 54. [6] _Hyp._ I. 121.