bject, unwilling to admit
the extreme probability of the hypothesis that, for every fact of
consciousness, whether in the domain of sense, of thought, or of emotion,
a certain definite molecular condition is set up in the brain; who does
not hold this relation of physics to consciousness to be invariable, so
that, given the state of the brain, the corresponding thought or feeling
might be inferred; or, given the thought or feeling, the corresponding
state of the brain might be inferred.

But how inferred? It is at bottom not a case of logical inference at all,
but of empirical association. You may reply that many of the inferences of
science are of this character; the inference, for example, that an
electric current of a given direction will deflect a magnetic needle in a
definite way; but the cases differ in this, that the passage from the
current to the needle, if not demonstrable, is thinkable, and that we
entertain no doubt as to the final mechanical solution of the problem. But
the passage from the physics of the brain to the corresponding facts of
consciousness is unthinkable. Granted that a definite thought and a
definite molecular action in the brain occur simultaneously; we do not
possess the intellectual organ, nor apparently any rudiment of the organ,
which would enable us to pass, by a process of reasoning, from the one to
the other. They appear together, but we do not know why. Were our minds
and senses so expanded, strengthened, and illuminated as to enable us to
see and feel the very molecules of the brain; were we capable of following
all their motions, all their groupings, all their electric discharges, if
such there be; and were we intimately acquainted with the corresponding
states of thought and feeling, we should be as far as ever from the
solution of the problem, "How are these physical processes connected with
the facts of consciousness?" The chasm between the two classes of
phenomena would still remain intellectually impassable. Let the
consciousness of _love_, for example, be associated with a right-handed
spiral motion of the molecules of the brain, and the consciousness of
_hate_ with a left-handed spiral motion. We should then know, when we
love, that the motion is in one direction, and when we hate, that the
motion is in the other; but the _Why?_ would remain as unanswerable as
before.

In affirming that the growth of the body is mechanical, and that thought,
as exercised by us, has its cor