To be fully understood, this conception must be taken along with the general theory of Evolution. Mr. Spencer argues that all things whatever are inevitably tending towards equilibrium; and that consequently the progress of mankind cannot cease until there is equilibrium between the human constitution and the conditions of human existence. Or, as he argues in _First Principles_ (Second Edition, p. 512), 'The adaptation of man's nature to the conditions of his existence cannot cease until the internal forces which we know as feelings are in equilibrium with the external forces they encounter. And the establishment of this equilibrium, is the arrival at a state of human nature and social organization, such that the individual has no desires but those which may be satisfied without exceeding his proper sphere of action, while society maintains no restraints but those which the individual voluntarily respects. The progressive extension of the liberty of citizens, and the reciprocal removal of political restrictions, are the steps by which we advance towards this state. And the ultimate abolition of all limits to the freedom of each, save those imposed by the like freedom of all, must, result from the complete equilibration between man's desires and the conduct necessitated by surrounding conditions.' The conduct proper to such a state, which Mr. Spencer thus conceives to be the subject-matter of Moral Science, truly so-called, he proposes, in the Prospectus to his _System of Philosophy_, to treat under the following heads. PERSONAL MORALS.--The principles of private conduct--physical, intellectual, moral, and religious--that follow from the conditions to complete individual life; or, what is the same thing, those modes of private action which must result from the eventual equilibration of internal desires and external needs. JUSTICE.--The mutual limitation of men's actions necessitated by their co-existence as units of a society--limitations, the perfect observance of which constitutes that state of equilibrium forming the goal of political progress. NEGATIVE BENEFICENCE.--Those secondary limitations, similarly necessitated, which, though less important and not cognizable by law, are yet requisite to prevent mutual destruction of happiness in various indirect ways: in other words--those minor self-restraints dictated by what may be called passive sympathy. POSITIVE BENEFICENCE.--Comprehending all modes of conduct, dictated by active sympathy, which imply pleasure in giving pleasure--modes of conduct that social adaptation has induced and must render ever more general; and which, in becoming universal, must fill to the full the possible measure of human happiness. * * * * *