IT is desirable that the present volume, the origin of
which is explained in the author's preface, should be accom-
panied by a brief statement in relation to Mr. Spencer's
other works upon sociological science.The " Principles of
Sociology" was projected by Mr. Spencer as a part of his
philosophical system, the publication of which was com-
menced in 1860. Five volumes of that system have ap-
peared, viz.: " First Principles," in one volume; the
" Principles of Biology," in two volumes; and the " Prin-
ciples of Psychology," in two volumes. " First Principles "
develops the general method of the philosophy to be carried
out in the subsequent works.In the two succeeding parts
that method is applied to the interpretation of the phenom-
ena of Life and Mind, the whole course of exposition being
preparatory to the " Principles of Sociology," in three vol-
umes, which are next in order.Upon this work Mr. Spen-
cer has now entered, and it will be published in quarterly
parts, by subscription, in the same form that was adopted
with the previous divisions of the work.

Several years since Mr. Spencer foresaw a difficulty that
would arise in working out the principles of social science
from a lack of the data or facts necessary as a basis of rea-
soning upon the subject; and he saw that, before the philos-
ophy could be elaborated, these facts must be systematically
and exhaustively collected.How early and how clearly Mr.
Spencer perceived the nature, diversity, and extent of the

-iii-