upon philosophical thought than it has by proving an
apparently quantitative relation between material changes and mental
changes. It has always been known that there is qualitative relation.
Even long before mankind suspected that the brain was in any way
connected with thought, it was well understood that alcohol and other
poisons exercised their sundry influences on the mind in virtue of
influences which they exercised upon the body; and even the lowest
savages must always have been aware that a blow on the head is followed
by insensibility. But it was not until the rise of Physiology that this
qualitative relation between corporeal changes and mental changes was
gradually found to be a quantitative one--or that every particular
change of mind had an exact and invariable counterpart in some
particular change of body. It is needless for me to detail the
successive steps in the long course of physiological discovery whereby
this great fact has been established; it is enough to say that the fact
_is_ established to the satisfaction of every physiologist.

Now, when once the relation between material changes and mental changes
has been thus recognized as quantitative--or, which is the same thing,
when once the association has been recognized as both invariable and
exact--there arises the question as to how this relation is to be
explained. Formally considered--or considered as a matter of logical
statement irrespective of the relative probabilities which they may
present, either to the minds of different individuals or to the general
intelligence of the race--it appears to me that the possible hypotheses
are here seven in number.

I. The mental changes may cause the material changes.

II. The material changes may cause the mental changes.

III. There may be no causation either way, because the association
may be only a phenomenal association--the two apparently diverse
classes of phenomena being really one and the same.

IV. There may be no causation either way, because the association
may be due to a harmony pre-established by a superior mind.

V. There may be no causation either way, because the association
may always be due to chance.

VI. There may be no causation either way, because the material
order may not have any real existence at all, being merely an ideal
creation of the mental order.

VII. Whether or not there be any causation either w