In common use almost every word has many shades of meaning, and therefore needs to be interpreted by the context.

Knowledge is our most powerful engine of production.

The most valuable of all capital is that invested in human beings

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

Civilized countries generally adopt gold or silver or both as money.

Political Economy or Economics is a study of mankind in the ordinary business of life.

But if inventions have increased man's power over nature very much, then the real value of money is better measured for some purposes in labour than in commodities.