Knowledge is our most powerful engine of production.

Capital is that part of wealth which is devoted to obtaining further wealth.

In the absence of any short term in common use to represent all desirable things, or things that satisfy human wants, we may use the term Goods for that purpose.

I admit that these terms and the diagrams connected with them repel some readers, and fill others with the vain imagination that they have mastered difficult economics problems, when really they have done little more than learn the language in which parts of those problems can be expressed, and the machinery by which they can be handled. When the actual conditions of particular problems have not been studied, such knowledge is little better than a derrick for sinking oil-wells erected where there are no oil-bearing strata.

Slavery was regarded by Aristotle as an ordinance of nature, and so probably was it by the slaves themselves in olden time.

The price of every thing rises and falls from time to time and place to place; and with every such change the purchasing power of money changes so far as that thing goes.

Though a simple book can be written on selected topics, the central doctrines of economics are not simple and cannot be made so.