, 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
"Timaeus," ch. 19.

The eye is a light-bearer, "made of that part of elemental fire which
does not burn, but sheds a mild light, like the light of day.... When
the light of the day meets the light which beams from the eye, then
light meets like, and make a homogeneous body; the external light
meeting the internal light, in the direction in which the eye looks. And
by this homogeneity like feels like; and if this beam touches any
object, or any object touches it, it transmits the motions through the
body to the soul, and produces that sensation which we call _seeing_....
And if (in sleep) some of the strong motions remain in some part of the
frame, they produce within us likenesses of external objects,... and
thus give rise to dreams.... As to the images produced by mirrors and by
smooth surfaces, they are now easily explained, for all such phenomena
result from the mutual affinity of the external and internal fires. The
light that proceeds from the face (as an object of vision), and the
light that proceeds from the eye, become one continuous ray on the
smooth surface."]

Now we have to divide the segment which represents intelligible things
in this way: The one part represents the knowledge which the mind gets
by using things as images--the other; that which it has by dealing with
the ideas themselves; the one part that which it gets by reasoning
downward from principles--the other, the principles themselves; the one
part, truth which depends on hypotheses--the other, unhypothetical or