34. THE METAPHYSICIAN AND THE MIND.--I have reserved for the next
chapter the first two points mentioned as belonging to the plain man's
doctrine of the mind. In what sense the mind may be said to be in the
body, and how it may be conceived to be related to the body, are topics
that deserve to be treated by themselves in a chapter on "Mind and
Body." Here I shall consider what the metaphysician has to say about
the mind as substance, and about the mind as nonextended and immaterial.

It has been said that the Lockian substance is really an "unknowable."
No one pretends to have experience of it; it is revealed to no sense;
it is, indeed, a name for a mere nothing, for when we abstract from a
thing, in thought, every single quality, we find that there is left to
us nothing whatever.

We cannot say that the substance, in this sense of the word, is the
_reality_ of which the qualities are _appearances_. In Chapter V we
saw just what we may legitimately mean by realities and appearances,
and it was made clear that an unknowable of any sort cannot possibly be
the reality to which this or that appearance is referred. Appearances
and realities are experiences which are observed to be related in
certain ways. That which is not open to observation at all, that of
which we have, and can have, no experience, we have no reason to call
the reality of anything. We have, in truth, no reason to talk about it
at all, for we know nothing whatever about it; and when we do talk
about it, it is because we are laboring under a delusion.

This is equally true whether we are concerned with the substance of
material things or with the substance of minds. An "unknowable" is an
"unknowable" in any case, and we may simply discard it. We lose
nothing by so doing, for one cannot lose what one has never had, and
what, by hypothesis, one can never have. The loss of a mere word
should occasion us no regret.

Now, we have seen that we do not lose the world of real material things
in rejecting the "Unknowable" (Chapter V). The things are complexes of
qualities, of physical phenomena; and the more we know about these, the
more do we know about real things.

But we have also seen (Chapter IV) that physical phenomena are not the
only phenomena of which we have experience. We are conscious of mental
phenomena as well, of the phenomena of the subjective order, of
sensations and ideas. Why not admit that these _constitute_ the mind,
as physic