h
which we call the rainbow a mere appearance (better, illusion), but the
combination of sun and rain which gives rise to this illusion the thing
in itself, as that which in universal experience and in all different
positions with respect to the senses, is thus and not otherwise determined
in intuition, or that which essentially belongs to the intuition of the
object, and is valid for every human sensibility (in antithesis to that
which only contingently belongs to it, and is valid only for a special
position or organization of this or that sense). Similarly an object always
appears to grow smaller as its distance increases, while in itself it is
and remains of some fixed size. And this use of words is perfectly
correct, in the _physical or empirical_ sense of "in itself"; but in the
_transcendental_ sense the raindrops, also, together with their form and
size, are themselves mere phenomena, the "in itself" of which remains
entirely unknown to us. Kant, moreover, does not wish to see the
subjectivity of the forms of intuition placed on a level with the
subjectivity of sensations or explained by this, though he accepts it as
a fact long established. The sensations of color, of tone, of temperature
are, no doubt, like the representation of space in that they belong only to
the subjective constitution of the sensibility, and can be attributed to
objects only in relation to our senses. But the great difference between
the two is that these sense qualities may be different in different persons
(the color of the rose may seem different to each eye), or may fail to
harmonize with any human sense; that they are not _a priori_ in the same
strict sense as space and time, and consequently afford no knowledge of the
objects of possible experience independently of perception; and that they
are connected with the phenomenon only as the contingently added effects of
a particular organization, while space, as the condition of external
objects, necessarily belongs to the phenomenon or intuition of them. _It is
through space alone that it is possible for things to be external objects
for us_. The subjectivity of sensation is individual, while that of space
and time is general or universal to mankind; the former is empirical,
individually different, and contingent, the latter _a priori_ and
necessary. Space alone, not sensation, is a _conditio sine qua non_ of
external perception. Space and time are the sole _a priori_ elements of
the sensi