The principle of human equality is founded on the metaphysical unity of mankind, which is revealed by a number of particular facts. The five essential preconditions and buttresses of human equality are: personality, objectivity, the unity of mankind, the element of partial equality, and the element of differences and variations. The principle of the unity of mankind is, however, directly important not only for 'international' relationships, but also for the inner structure of a circumscribed social unity, such as a nation or state. However, equality between men also follows conclusively and very convincingly from human inequality itself. The nature of this inequality is so diverse and variable, that it resists any firm classification and differentiation. Thus, the doctrine of inequality is fragmented and ambiguous. This does not refute it, of course, but, at all events, casts doubt on these hasty theoretical conclusions drawn from the facts of inequality.