These words are alike in referring, most specifically, to a bargaining for goods or services that is conducted without the use of money.

Barter is the most formal and most specific of these. In the most primitive economic system, one gives the product he has made or grown in return for someone else’s product ?with no intermediary devices to assess abstract value. A farmer, in such a system, might barter several sacks of fodder for a pair of boots made by a shoemaker who happens to need feed for his horse. Barter in this strict definition does not involve middlemen; a person barters only for what he needs and intends to use. If the shoemaker, however, didn’t need fodder at the exact moment of his bargain, he might still take the fodder, planning to trade it with someone else for something he could use. In any but the most primitive societies, of course, bartering as such, except among children, is almost unknown, but many kinds of trading may exist. A person may trade merely for sustenance, as with barter , but more commonly in order to sell what he gets for a profit; trading , thus, can be an occupation or livelihood: a record number of shares traded on the Stock Exchange. In senses other than the economic, barter was fewer uses than trade , and would strike most ears as needlessly formal: diplomats who bartered for peace. Trade , more informal, also has a wider range of general application: trading compliments; trading glances in the crowded bar.

In bartering and trading , a person must exchange one item for another. Exchanges is not limited to the economic sense applying to any reciprocal giving and receiving. In some uses, the things given and received may be equally valued: exchanging partners at a dance. Or the value may not be an important aspect: exchanging gifts at Christmas; exchanging letter. Perhaps more often, exchange implies the divesting of something unsuitable or unsatisfactory for something better: exchanging jobs; exchanging merchandise damaged in delivery.

Swap , most specifically, is like barter , except for its extreme informality.

• The prospector swapped his gold dust for a jug of whisky; I’ll swap my shanghai for your mouth organ.

In some cases it may enter formal speech or writing when descriptive of a specific phenomenon: The sociologist did research on housewives who swapped husbands at Saturday night parties.