No slave system has ever been able to continue to function on the slaves provided by its own biological reproduction because the rate of human reproduction is too slow and the expense from infant mortality and years of unproductive upkeep of the young make this prohibitively expensive. This relationship is one of the basic causes of the American Civil War, and was even more significant in destroying ancient Rome.

The backwardness of our religious and social developments is undoubtedly holding back the development of the intellectual and political levels.

No scientist ever believes that he has the final answer or the ultimate truth on anything.

The history of the last century shows, as we shall see later, that the advice given to governments by bankers, like the advice they gave to industrialists, was consistently good for bankers, but was often disastrous for governments, businessmen, and the people generally.

It is clear that every civilization undergoes a process of historical change. We can see that a civilization comes into existence, passes through a long experience, and eventually goes out of existence.

A civilization is complicated, in the first place, because it is dynamic; that is, it is constantly changing in the passage of time, until it has perished.

The social sciences are usually concerned with groups of persons rather than individual persons. The behavior of individuals, being free, is unpredictable.