catallactics: The science of exchanges, either with or without money. Popularly known as economics (or part of it). The word was coined by Richard Whately in 1831 as a better description of this study than "political economy", as the science was then known.

cardinal number: One of the natural numbers, 1, 2, 3, 4, ... Mises uses the term rather loosely, to refer to rational numbers, and even real numbers. Specifically, he says that man's mental valuation process, by means of which he prefers one thing to another, is not susceptible to analysis using cardinal numbers. See also ordinal number

direct exchange: Barter. The direct exchange of goods or services without using money. Primitive societies presumably had barter economies based on direct exchange. Mises cautions us that we must take care to understand that money, the medium of exchange, is not a neutral element in real world exchanges.

epigones: Acolytes, or disciples, especially inferior imitators of the original.

indirect exchange: The act of buying or selling goods or services for money. Economic calculation is only possible in a market society dominated by acts of indirect exchange. Economic calculation is always performed in terms of money. See also direct exchange.

ordinal number: A number used to represent how far along in a list of things a particular item is found. For instance, in the set {a, b, c, d} a is the first item, b is the seconnd item, and d is the fourth item. For finite sets, there is a direct connection betwwen a cardinal number and its corresponding ordinal. In theory, the values acting man attaches to various ends may be described in terms of ordinal numbers. In practice, the possibilities open to a man at an instant of time are limited, so one never really considers the totality of one's wants and desires. See also cardinal number.