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

Consumption may be regarded as negative production.

Today as always, men fall into two groups: slaves and free men. Whoever does not have two-thirds of his day for himself, is a slave, whatever he may be: a statesman, a businessman, an official, or a scholar.

Technical people don't make good slaves. Without their wholehearted cooperation, things fall apart.

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.

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.