tory is essentially a history of his
opinions; and these are subject to the fundamental psychological law.

It must, however, be observed that all branches of knowledge are not in
the same stage simultaneously. Some may have reached the metaphysical,
while others are still lagging behind in the theological; some may have
become scientific, while others have not passed from the metaphysical.
Thus the study of physical phenomena has already reached the positive
stage; but the study of social phenomena has not. The central aim of
Comte, and his great achievement in his own opinion, was to raise the
study of social phenomena from the second to the third stage.

When we proceed to apply the law of the three stages to the general
course of historical development, we are met at the outset by the
difficulty that the advance in all the domains of activity is not
simultaneous. If at a given period thought and opinions are partly
in the theological, partly in the metaphysical, and partly in the
scientific state, how is the law to be applied to general development?
One class of ideas, Comte says, must be selected as the criterion, and
this class must be that of social and moral ideas, for two reasons.
In the first place, social science occupies the highest rank in the
hierarchy of sciences, on which he laid great stress. [Footnote: Cours
de phil. pos. v. 267. Law of consensus: op. cit. iv. 347 sqq., 364, 505,
721, 735.] In the second, those ideas play the principal part for the
majority of men, and the most ordinary phenomena are the most important
to consider. When, in other classes of ideas, the advance is at any time
more rapid, this only means an indispensable preparation for the ensuing
period.

The movement of history is due to the deeply rooted though complex
instinct which pushes man to ameliorate his condition incessantly, to
develop in all ways the sum of his physical, moral, and intellectual
life. And all the phenomena of his social life are closely cohesive,
as Saint-Simon had pointed out. By virtue of this cohesion, political,
moral, and intellectual progress are inseparable from material progress,
and so we find that the phases of his material development correspond to
intellectual changes. The principle of consensus or "solidarity," which
secures harmony and order in the development, is as important as the
principle of the three stages which governs the onward movement. This
movement, however, is not in a right lin