Then the answer given is firmly established upon the doctrine of a gradual unfolding of the mental faculties in obedience to natural law, the unfolding taking the form of a double-sided change from the simple to the complex, and from the indefinite to the definite. So is it with all other subjects whatsoever. In the essay on Manners and Fashions, for example, emphasis is laid upon the truths that the various forms of restraint exercised by society as an aggregate over its individual members — such restraints being now clearly differentiated into ecclesiastical, political, and ceremonial — are all natural developments from one primordial form, and that the divergence of one from the other and of all from such primordial form takes place "in conformity with the laws of evolution of all organized bodies." And once again a similar line of argument is followed out in the extremely attractive articles on the Genesis of Science and The Origin and Function of Music. Finally, in the elaborate essay on Progress: its Law and Cause, evolutionary principles are enunciated with the utmost distinctness. The law of progress is shown to consist in the transformation of the homogeneous into the heterogeneous (a partial statement afterward completed by the addition of a factor for the time being overlooked); and this process is illustrated by examples taken from all orders of phenomena, while the cause of the transformation is found in the law of the multiplication of effects, afterward brought out more fully in First Principles. In this essay, too, as in that on the Development Hypothesis, the general law of evolution is presented as holding good in the production of species and varieties, though here again direct adaptation to the conditions of existence is the only factor recognized as playing a part in the stupendous drama of unfolding life.
I have said enough, I think, to show how active was the period with which we have just been dealing — active alike in original production and in the absorption of fresh material and the organization of new ideas. But the enumeration of these five-and-twenty essays does not exhaust the record of Spencer's labors during this time. His studies in psychology, of which the essays on The Universal Postulate (1853) and The Art of Education (1854) were the immediate results, took more systematic form about the date of the publication of the latter paper; and in 1855 the first edition of his Principles of Psychology made its appearance. As this work was subsequently included as a portion of the two volumes on the Principles of Psychology in the synthetic system, any analysis of its contents does not fall within the scope of the present paper. Two remarks may, however, be appropriately made
- This additional factor being increase in definiteness. A change must consist in increasing heterogeneity and increasing definiteness, to constitute evolution.