Each appearance, then, must be referred to some particular real thing and not to any other.  This is true of the appearances which we recognize as such in common life, and it is equally true of the appearances recognized as such in science.  The pen which I feel between my fingers I may regard as appearance and refer to a swarm of moving atoms.  But it would be silly for me to refer it to atoms “in general.”  The reality to which I refer the appearance in question is a particular group of atoms existing at a particular point in space.  The chemist never supposes that the atoms within the walls of his test-tube are identical with those in the vial on the shelf.  Neither in common life nor in science would the distinction between appearances and real things be of the smallest service were it not possible to distinguish between this appearance and that, and this reality and that, and to refer each appearance to its appropriate reality.  Indeed, it is inconceivable that, under such circumstances, the distinction should have been drawn at all.

These points ought to be strongly insisted upon, for we find certain philosophic writers falling constantly into a very curious abuse of the distinction and making much capital of it.  It is argued that what we see, what we touch, what we conceive as a result of scientific observation and reflection—­all is, 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.”