The term Quid Pro Quo is an old Latin saying and “principle of law”. The meaning is: An equal exchange or substitution. Latin quid, what? + pro, for + quo, ablative of quid, what?.

Explanation

Quid pro quo (Latin for “this for that”) is a legal principle and economic principle according to which a person who gives something should receive an appropriate consideration in return. It is comparable to the Latin proverbs manus manum lavat (“one hand washes the other”) and do ut des (“I give so that you give”).

Uses

Quid pro quo is used in sociology and game theory as an explanatory approach to explain cooperative behavior among egoists (cf. Homo economicus).

Quid pro quo (quid pro quo?, literally “what for whom?”) also means the accidental mixing up of two things[1][2], and quiproquo (“who for whom?”) means the confusion of two people.

Quid pro quo was also used in pharmacy as a term to express the pharmacist's ability to replace, or substitute, certain components of a preparation with others. Such substitution was already known in the Middle Ages, and corresponding substitutes were also published in medical literature, such as the Lorsch Pharmacopoeia and the Circa instans.