, in the last analysis, material
which is given us in sensation. The various senses furnish us with
different classes of sensations; we work these up into certain
complexes. But sensations are only the impressions which something
outside of us makes upon us. Hence, although we seem to ourselves to
know the external world as it is, our knowledge can never extend beyond
the impressions made upon us. Thus, we are absolutely shut up to
_appearances_, and can know nothing about the _reality_ to which they
must be referred.

Touching this matter Herbert Spencer writes[1] as follows: "When we are
taught that a piece of matter, regarded by us as existing externally,
cannot be really known, but that we can know only certain impressions
produced on us, we are yet, by the relativity of thought, compelled to
think of these in relation to a cause--the notion of a real existence
which generated these impressions becomes nascent. If it be proved
that every notion of a real existence which we can frame is
inconsistent with itself,--that matter, however conceived by us, cannot
be matter as it actually is,--our conception, though transfigured, is
not destroyed: there remains the sense of reality, dissociated as far
as possible from those special forms under which it was before
represented in thought."

This means, in plain language, that we must regard everything we know
and can know as appearance and must refer it to an unknown reality.
Sometimes Mr. Spencer calls this reality the Unknowable, sometimes he
calls it the Absolute, and sometimes he allows it to pass by a variety
of other names, such as Power, Cause, etc. He wishes us to think of it
as "lying behind appearances" or as "underlying appearances."

Probably it has already been remarked that this Unknowable has brought
us around again to that amusing "telephone exchange" discussed in the
third chapter. But if the reader feels within himself the least
weakness for the Unknowable, I beg him to consider carefully, before he
pins his faith to it, the following:--

(1) If we do perceive external bodies, our own bodies and others, then
it is conceivable that we may have evidence from observation to the
effect that other bodies affecting our bodies may give rise to
sensations. In this case we cannot say that we know nothing but
sensations; we know real bodies as well as sensations, and we may refer
the sensations to the real bodies.

(2) If we do not perceive that we have