d, not necessarily all our
Thoughts, but all the materials of Discourse, all that constitutes the
essence of Knowledge.

Our purpose at the moment is to show that this view is altogether false,
and our counter proposition is, that it is from our Activity that we
derive our fundamental conceptions of the external world; that
sensations only mark the interruptions in the dynamic Activity in which
we as potent beings partake, and that they serve therefore to denote and
distinguish our Experience, but do not constitute its essence.

We do not propose now to devote any time to the work of showing that
sensations from their very nature could never become the instruments of
Knowledge. We propose rather to turn to the principal ideas of the
external world which are the common equipment of the Mind in order to
ascertain whether in point of fact they are derived from Sensation.

Of course to some extent the answer depends on what we mean by
Sensation. If by that term we intend our whole Experience of the
external, then of course it necessarily follows--or, at least, we
admit--that our Knowledge of the external must be thence derived. But
such a use of the term is loose, misleading, and infrequent. The only
safe course is to confine the term Sensation to the immediate data of
the five senses--touch, sight, hearing, smell, and taste, with probably
the addition of muscular and other internal feelings. It is in this
sense that the word is usually employed, and has been employed by the
Sensationalist School themselves.

Now we might perhaps begin by taking the idea of Time as a concept
constantly employed in Discourse, but of which it would be absurd to
suggest that it is supplied to us by Sensation. It might, however, be
urged in reply that the idea of Time is not derived from the external
world at all, but is furnished to us directly by the operations of the
Mind, and that therefore its intellectual origin need not involve any
exception to the general rule that the materials of our Knowledge of the
world are furnished by Sensation alone. Without, therefore, entering
upon any discussion of the interesting question as to what is the real
nature of Time, we shall pass to the idea of Space.

Mach, the writer whom we have already quoted, in his essay on _Space and
Geometry_ speaks constantly and freely of sensations of Space, and as
there can be no denial of the fact that Space is a constituent of the
external world, it would seem t