(1) The monist may be a materialist; he may be an idealist; he may be neither.  In the last case, he may, with Spinoza, call the one Substance God; that is, he may be a Pantheist.  On the other hand, he may, with Spencer, call it the Unknowable, and be an Agnostic.  Other shades of opinion are open to him, if he cares to choose them.

(2) It does not seem wise to assent hastily to such statements as; “The universe is the manifestation of one unitary Being”; or:  “Mind and matter are the expression of one and the same principle.”  We find revealed in our experience mental phenomena and physical phenomena.  In what sense they are one, or whether they are one in any sense,—­this is something to be determined by an examination of the phenomena and of the relations in which we find them.  It may turn out that the universe is one only in the sense that all phenomena belong to the one orderly system.  If we find that this is the case, we may still, if we choose, call our doctrine monism, but we should carefully distinguish such a monism from those represented by Hoeffding and Spencer and many others.  There seems little reason to use the word, when the doctrine has been so far modified.

58.  DUALISM.—­The plain man finds himself in a world of physical things and of minds, and it seems to him that his experience directly testifies to the existence of both.  This means that the things of which he has experience appear to belong to two distinct classes.

It does not mean, of course, that he has only two kinds of experiences.  The phenomena which are revealed to us are indefinitely varied; all physical phenomena are not just alike, and all mental phenomena are not just alike.

Nevertheless, amid all the bewildering variety that forces itself upon our attention, there stands out one broad distinction, that of the physical and the mental.  It is a distinction that the man who has done no reading in the philosophers is scarcely tempted to obliterate; to him the world consists of two kinds of things widely different from each other; minds are not material things and material things are not minds.  We are justified in regarding this as the opinion of the plain man even when we recognize that, in his endeavor to make clear to himself what he means by minds, he sometimes speaks as though he were talking about something material or semi-material.

Now, the materialist allows these two classes to run together; so does the idealist.  The one says that everything is matter; the other, that everything is mind.  It would be foolish to maintain that nothing can be said for either doctrine, for men of ability have embraced each.  But one may at least say that both seem to be refuted by our common experience of the world, an experience which, so far as it is permitted to testify at all, lifts up its voice in favor of Dualism.

Dualism is sometimes defined as the doctrine that there are in the world two kinds of substances, matter and mind, which are different in kind and should be kept distinct.  There are dualists who prefer to avoid the use of the word substance, and to say that the world of our experiences consists of physical phenomena and of mental phenomena, and that these two classes of facts should be kept separate.