These primitive intuitions--the simple perceptions of sense, and the _à priori_ intuitions of the reason, which constitute the elements of all our complex notions, have essentially _diverse objects_--the sensible or ectypal world, seen by the eye and touched by the hand, which Plato calls δοξαστήν--_the subject of opinion_; and the noetic or archetypal world, perceived by reason, and which he calls διανοητικήν--_the subject of rational intuition or science_. "It is plain," therefore, argues Plato, "that _opinion_ is a different thing from _science_. They must, therefore, have a different _faculty_ in reference to a different object--science as regards that which _is_, so as to know the nature of real _being_--opinion as regards that which can not be said absolutely to be, or not to be. That which is known and that which is opined can not possibly be the same,... since they are naturally faculties of different things, and both of them are faculties--_opinion_ and _science_, and each of them different from the other."[529] Here then are two grand divisions of the mental powers--a faculty of apprehending universal and necessary Truth, of intuitively beholding absolute Reality, and a faculty of perceiving sensible objects, and of judging according to appearance. [Footnote 529: Ibid., bk. v. ch. xxi., xxii.] According to the scheme of Plato, these two general divisions of the mental powers are capable of a further subdivision. He says: Consider that there are two kinds of things, the _intelligible_ and the _visible_; two different regions, the intelligible world and the sensible world. Now take a line divided into two equal segments to represent these two regions, and again divide each segment in the same ratio--both that of the visible and that of the intelligible species. The parts of each segment are to represent differences of clearness and indistinctness. In the visible world the parts are _things_ and _images_. By _images_ I mean shadows,[530] reflections in water and in polished bodies, and all such like representations; and by _things_ I mean that of which images are resemblances, as animals, plants, and things made by man. You allow that this difference corresponds to the difference of _knowledge_ and _opinion_; and the _opinionable_ is to the _knowable_ as the _image_ to the _reality_.[531] [Footnote 530: As in the simile of the cave ("Republic," bk. vii. ch. i. and ii.).] [Footnote 531: The analogy between the "images produced by reflections in water and on polished surfaces" and "the images of external objects produced in the mind by sensation" is more fully presented in the "Timæus," ch. 19.