Once more it must be admitted that the meaning of "private ownership" and "social possession" will vary exceedingly in each age. When private dominion has become exceedingly individual and practically absolute, the opposition between the two terms will necessarily be very sharp. But in those earlier stages of national and social evolution, when the community was still regarded as composed, not of persons, but of groups, the antagonism might be, in point of theory, extremely limited; and in concrete cases it might possibly be difficult to determine where one ended and the other began. Yet it is undeniable that socialism in itself need mean no more than the central principle of State-ownership of capital and land. Such a conception is consistent with much private property in other forms than land and capital, and will be worked out in detail differently by different minds. But it is the principle, the essence of it, which justifies any claims made to the use of the name. We may therefore fairly call those theories socialistic which are covered by this central doctrine, and disregard, as irrelevant to the nature of the term, all added peculiarities contributed by individuals who have joined their forces to the movement. By socialistic theories of the Middle Ages, therefore, we mean no more than those theories which from time to time came to the surface of political and social speculation in the form of communism, or of some other way of bringing about the transference which we have just indicated. But before plunging into the tanglement of these rather complicated problems, it will make for clearness if we consider quite briefly the philosophic heritage of social teaching to which the Middle Ages succeeded.