The Metaphysics of a Naturalist 
27 
physical and psychical. Two forms of this theory are possible, 
the one assumes that matter is the only real thing and that the 
so-called spiritual phenomena are only properties of matter. 
Materialism finds no evidence of a second reality aside from the 
matter of a body. Its spirit can at most be but an abstraction or 
a special way of considering the properties of matter itself, which 
is fully competent to explain all the peculiarities of the conscious 
life. On the other hand, spiritualism replies that all that we 
know consists of sensations and other forms of psychical mani- 
festation and that matter is only an unjustifiable inference. 
The properties of matter, such as extension and inertia, are names 
for the constant form of our experiences. The second form of the 
identity theory is more likely to appeal to the thoughtful student 
than the first, yet it is in several respects unsatisfying to the 
critical mind. 
The commonest way of attempting a reconciliation of the 
difficulties above noted at the present time is by the supposition 
that the same process may have two aspects. Fechner compared 
the -nervous and the psychical to the outer and the inner aspects of 
a curve. Seen from without it is convex; seen from within, it is 
concave. A concave line is different from a convex one, but 
yet they seem to be one and the same line viewed from different 
points of view. This is a clever illustration, but it must not be 
forgotten that it is only an illustration and is not an explanation. 
Outside and inside of a curve are mathematical ideas implying, 
among other things, certain points of reference or loci without 
which such a distinction as that between the outside and the 
inside of a curve is impossible. To press the illustration is to 
to be guilty of a subtle form of begging the question, for it is 
this difference between the inside and the outside point of view 
that is sought to be defined. 
Let us see if we may not adjust the difficulties of this problem 
in a way that, while it shall not assume to offer a solution of a 
problem in its nature to us insoluble, yet shall leave us in a state 
of greater satisfaction with the practical relation of man to the 
two forms in which his experience appeals to him. First, then, 
the only absolute criterion of being we know is change or activity. 
A non-acting thing is nothing. Even an imaginary thing is 
an active thing. In our own experience of our purest acts we 
are unconscious of anything back of the act producing the act. 
We seem to will spontaneously. Pure activity without the ele- 
