When goods are exchanged between countries, they must be paid for by commodities or gold. They cannot be paid for by the notes, certificates, and checks of the purchaser's country, since these are of value only in the country of issue.

I came into history from a primary concern with mathematics and science. This has been a tremendous help to me as a person and as a historian, although it must be admitted it has served to make my historical interpretations less conventional than may be acceptable of many of my colleagues in the field.

The problem of meaning today is the problem of how the diverse and superficially self-contradictory experiences of men can be put into a consistent picture that will provide contemporary man with a convincing basis from which to live and to act.

The instrument of expansion of Classical civilization was a social organization, slavery.

For years I have told my students that I been trying to train executives rather than clerks. The distinction between the two is parallel to the distinction previously made between understanding and knowledge. It is a mighty low executive who cannot hire several people with command of more knowledge than he has himself.

The basis of social relationships is reciprocity: if you cooperate with others, others will cooperate with you.

Each individual in a society is a nexus where innumerable relationships of this character intersect.