Of course the family is a step leading up to the tribal stage of morality, and it may be that the idea of incest marks the social stage in which the moral sphere was conterminous with the family, corresponding to the institution of exogamy in the moral system of the tribe. It may be added that even in the modern family the feeling which unites the members often consists less, very much less, of affection than of a sort of obligation to hang together for mutual defence. FOOTNOTES: [Footnote 2: Cf. Plato's myth of Protagoras (_Prot_. 322 B ff.).] Sec. 7 The City State The City State, self-contained, self-supporting, truly democratic, is marked by a similar pugnacity. Only full citizenship conferred full moral rights, and any ferocity could be justified in war against another city. Athens wore herself out in the long struggle with Sparta, and Greece was lured to destruction by the devil of Imperialism, whose stock argument is to suggest that a State can extend its rights without extending its obligations. But the limitation of the moral sphere by the boundaries of the city is less apparent in the Greek States, because in the historical period at least they were already in transition to a larger view, and enlightened opinion certainly believed in a moral system which should include all Greek States, to the exclusion of course of all "barbarians": but this larger view was even more definitely limited, and the demarcation of those within from those outside the moral sphere was never more sharply conceived, than in the difference commonly held to exist between Greeks and Barbarians. Yet even so Greece can maintain her pre-eminence in thought; for Plato and Euripides at least glimpsed the conception, by which we do not yet consent to be guided, of the moral equality of all mankind.[3] For all these reasons the City State as a limited moral sphere is better seen perhaps in Mediaeval Italy, where, I imagine, a Florentine might kill a native of Pisa whenever he liked; whereas if he killed a fellow Florentine he risked at least the necessity of putting himself outside the moral sphere, of having that is to leave Florence and stay in Pisa till the incident was forgotten.[4] FOOTNOTES: [Footnote 3: Even Aristotle probably had some suspicion of it; so in his anxiety to justify the institution of slavery he had to make out that slaves were not men at all but only machines.]