The Platonic Sokrates (as I remarked above) lays down as the fundamental, generating, principle of human society, the reciprocity of need and service, essentially belonging to human beings: exchange of services is indispensable, because each man has many wants more than he can himself supply, and thus needs the services of others: while each also can contribute something to supply the wants of others. To this general principle Plato gives a peculiar direction. He apportions the services among the various citizens; and he provides that each man shall be specialised for the service to which he is peculiarly adapted, and confined to that alone. No double man[1] is tolerated. How such specialisation is to be applied in detail among the multitude of cultivators and other producers, Plato does not tell us. Each is to have his own employment: we know no more. But in regard to the two highest functions, he gives more information: first, the small cabinet of philosophical Elders,[2] Chiefs, or Rulers--artists in the craft of governing, who supply professionally that necessity of the Commonwealth, and from whom all orders emanate: next, the body of Guardians, Soldiers, Policemen, who execute the orders of this cabinet, and defend the territory against all enemies. Respecting both of these, Plato carefully prescribes both the education which they are to receive, and the circumstances under which they are to live. They are to be of both sexes intermingled, but to know neither family nor property: they live together in barrack, and with common mess, receiving subsistence and the means of decent comfort, but no more, from the producers: respecting sexual relations and births, I shall say more presently. [Footnote 1: Plato, Rep. iii. p. 397 E.] [Footnote 2: The principle laid down in the Protagoras will be remembered--[Greek: ei(=s e)/chôn te/chnên polloi=s i(kano\s i)diô/tais] (Protag. p. 322 D).] [Side-note: The four cardinal virtues are assumed as constituting the whole of Good or Virtue, where each of these virtues resides.]