We bring to an end our review of the "Synthetic Philosophy" by pointing out that the ethical doctrine constituting the culmination of the system which is set forth in the "Principles of Ethics" is fundamentally a corrected and elaborated version of the doctrine propounded in "Social Statics" issued as long ago as 1850. The correspondence between the two works is shown not only by the coincidence of their constructive divisions, but also by the agreement of their cardinal ideas. As in the one, so in the other, Man, in common with lower creatures, is held to be capable of indefinite change by adaptation to conditions. In both he is regarded as undergoing transformation from a nature appropriate to his aboriginal wild life, to a nature appropriate to a settled civilized life; and in both this transformation is described as a moulding into a form fitted for harmonious co-operation. In both works, too, this moulding is said to be effected by the repression of certain primitive traits no longer needed, and the development of needful traits. As in the first work, so in this last, the great factor in the progressive modification is shown to be sympathy. It was contended in "Social Statics," as it is contended in the "Principles of Ethics," that harmonious social co-operation implies that limitation of individual freedom which results from sympathetic regard for the freedoms of others; and that the law of equal freedom is the law in conformity to which equitable individual conduct and equitable social arrangements co-exist. Mr. Spencer's theory in 1850 was, as his theory still is, that the mental products of Sympathy which constitute what is called "the moral sense," arise as fast as men are disciplined into social life; and that along with them arise intellectual perceptions of right human relations, which become clearer as the form of social life becomes better. Further, in the earlier work it was inferred, as it is inferred in the latest, that there is being effected a conciliation of individual natures with social requirements; so that there will eventually be achieved the greatest individuation, along with the greatest mutual dependence,--an equilibrium of such kind that each, in fulfilling the wants of his own life, will aid in fulfilling the wants of all other lives. We observe, finally, that, in the first work, there were drawn essentially the same corollaries respecting the rights of individuals and their relations to the State that are drawn in the "Principles of Ethics."