8 
4. The doctrine of evolution has its attractions, not only 
for those who feel an interest in the labors of the naturalist and 
the physiologist, but also for those engaged in psychological 
studies. And, within the last twenty years, a theory of the 
evolution of mind has gained considerable currency. To 
say that the state of the mind and that of the body are mutually 
symbolic might seem to be going too far ; for there are bodily 
processes of which we are unconscious, and, in speaking of mind, 
we generally mean conscious mind. Let us, for the present, 
however, accept the proposition that the state of the mind and. 
that of the brain are mutually symbolic, including, if necessary, 
in the word “ brain ” all parts of the body essential to constitute 
the state symbolized in the mental state. Now, even if a state of 
the brain were exactly known, if the position and motion of each 
of its particles and the physical influences to which each was 
subject were rigorously determined, and if the corresponding 
mental state were known with the like accuracy, we still could 
say no more than that each state was a symbol of the other, and 
we should be as far as ever from knowing what mind in itself is, 
or how its manifestations are connected with those of matter. 
Understanding by ‘ similar’ precisely similar, and speaking of 
course of living organisms, suppose that it were possible to find 
two brains which, as well as their corresponding bodies, should 
be, at a given instant, under similar external conditions and in 
similar states, such state in one case being, and in the other case 
not being, accompanied by consciousness ; would the consecutive 
state of the two brains and bodies be similar ? I conceive that, 
in order to justify the assumption that the relation between 
cerebral and mental states, is, for us, simply a symbolic one, — it 
is not necessary to answer this question ; and, that whether we 
answer it in the affirmative or the negative, the assumption may 
be justified. If we say that the consecutive states would be 
similar, no question arises. If it be objected, that the consecu- 
tive states would not be similar, the objection implies that the 
superaddition of consciousness to life introduces a new physical 
or natural force into the bodily system. Por brevity, and with- 
out any reference to the supposed cause of certain alleged 
manifestations which have been termed spiritualistic, call this 
hypothetical new force, psychical force, or psychism. Concede 
the existence of psychism, and even that, if difficulties about 
energy arose, they might perhaps be explained by some such 
theory as one which should suppose psychism to act at a distance 
with a force depending on its velocity, and therefore not subject 
to the law of conservation of energy. Still, the chasm which 
exists in thought between matter and mind would not be 
bridged over. If the consecutive state of the unconscious 
machine could be determined from the postulated conditions, so, 
too, could that of the machine to which consciousness was super- 
added ; the only difference being that, in determining the con- 
secutive state ot the latter, we should have to consider the effect 
of a new natural force, possibly not differing more from the old 
