ct, the causes of human conduct
being only approximately known. Hence it is impossible to predict _with
scientific accuracy_ any one man's acts, resulting as they do partly
from his circumstances, which, in the future, cannot be precisely
foreseen, and, partly, from his character, which can never be exactly
calculated, because the causes which have determined it are sure, in the
aggregate, not to be entirely like those which have determined any other
man's. But approximate generalisations, though only probably true as to
the acts and characters of individuals, will be certainly true as to
those of masses, whose conduct is determined by general causes chiefly;
and they are therefore sufficient for political and social science. They
must, however, be connected deductively with the universal laws of human
nature on which they rest, or they will be only low empirical laws. This
is the text of the next two chapters.

CHAPTER IV.

THE LAWS OF MIND.

By the laws of mind (i.e. as considered in this treatise, the laws of
mental phenomena) are meant the laws according to which one state of
mind is produced by another. If M. Comte and others be right in saying
that, in like manner with the mental phenomena called sensations, all
the other states of mind have for their proximate causes nervous states,
there would be no original laws of mind, and Psychology would be a mere
branch of Physiology. But at present, this tenet is not proved, however
highly probable; and, at all events, the characteristics of those
nervous states are quite unknown; consequently the uniformities of
succession among the mental phenomena, which undoubtedly do exist, and
which are not proved to result from more general laws, must be
considered as the subject of a distinct science called Psychology. We
can ascertain only by experiment the simple laws of Mind, such as--1.
That a state of consciousness can be reproduced in the absence of the
cause which first excited it (i.e. that every mental impression has its
idea), and--2. That these secondary mental states themselves are
produced according to the three laws of ideas. But the complex laws are
got from these simple laws, according either to the Composition of
Causes, when the complex idea is said to _consist of_ the Simple Ideas,
or to chemical combination, when it is said to be _generated by_ them.
Hartley and Mr. James Mill indeed hold _all_ the mental phenomena to be
generated by chemical combina