main argument.

Time, however, according to Kant, differs from space in one important
respect. It is the form not of outer but of inner sense; in other
words, while space is the form under which we perceive things, time is
the form under which we perceive ourselves. It is upon this difference
that attention must be concentrated. The existence of the difference
at all is upon general grounds surprising. For since the arguments by
which Kant establishes the character of time as a form of perception
run _pari passu_ with those used in the case of space, we should
expect time, like space, to be a form under which we perceive things;
and, as a matter of fact, it will be found that the only _argument_
used to show that time is the form of inner, as opposed to outer,
sense is not only independent of Kant's general theory of forms of
sense, but is actually inconsistent with it.[2] Before, however, we
attempt to decide Kant's right to distinguish between inner and outer
sense, we must consider the facts which were before Kant's mind in
making the distinction.

[2] B. 49 (b), M. 30 (b). See pp. 109-12.

These facts and, to a large extent, the frame of mind in which Kant
approached them, find expression in the passage in Locke's _Essay_,
which explains the distinction between 'ideas of sensation' and 'ideas
of reflection'.

"Whence has it [i. e. the mind] all the materials of reason and
knowledge? To this I answer, in one word, from experience.... Our
observation, employed either about external, sensible objects, or
about the internal operations of our minds, perceived and reflected
on, by ourselves, is that which supplies our understandings with all
the materials of thinking. These two are the fountains of
knowledge...."

"First, Our senses, conversant about particular sensible objects, do
convey into the mind several distinct perceptions of things, according
to those various ways, wherein those objects do affect them: and thus
we come by those ideas we have of Yellow, White, Heat, Cold, Soft,
Hard, Bitter, Sweet, and all those, which we call sensible qualities;
which, when I say the senses convey into the mind, I mean, they, from
external objects, convey into the mind what produces there those
perceptions. This great source of most of the ideas we have, depending
wholly upon our senses, and derived by them to the understanding, I
call _sensation_."

"Secondly, The other fountain, from which experience furnisheth the