English Reference
Idiom idiom

quid pro quo

C1 Roman origin
Meaning

Something given in return for something else, usually as an understood trade.

Examples
SIMPLE

“I'll cover your shift, but there's a quid pro quo.”

CONTEXTUAL

“The support was offered without conditions, though everyone understood the quid pro quo.”

COMPLEX

“No quid pro quo was ever stated, which is the entire difficulty with proving one: the arrangement consisted of two decisions taken four months apart by people who had had lunch in between.”

Origin

The phrase started in the pharmacy. Quid pro quo — this for that — was the medieval apothecary's term for substituting one ingredient for another when the prescribed one was unavailable. It could be perfectly legitimate and it could kill you, and the earliest English uses carry that unease: a quid pro quo was something passed off in place of the real thing.

By the sixteenth century the sense had shifted to a fair exchange, and Roman legal thinking underlies where it went next. Contract in Roman law turned on reciprocity — an obligation that ran only one way was hard to enforce — and English law developed its own version of the requirement, which is why the phrase settled so comfortably into legal English.

Its modern flavour is transactional and slightly compromising. A quid pro quo is rarely a purchase; it is a favour with an unspoken invoice attached.

The Law's Latinconnected storiesSee all Roman origin →

Roman legal Latin that never left the courtroom — or the boardroom.

  1. 01

    bona fide (idiom)

    Genuine and honestly meant — the real thing, not a pretence.

    The Roman standard of good faith.
  2. 02

    caveat emptor (idiom)

    Let the buyer beware — checking what you are buying is your own problem.

    What Rome did not actually say.
  3. 03

    de facto (idiom)

    In practice, whatever the official position says.

    The question of fact.
  4. 04

    de jure (idiom)

    According to the law, whether or not that is what actually happens.

    The question of law.
  5. 05

    ipso facto (idiom)

    By that very fact — the consequence follows automatically, with no further step.

    Consequences that need no hearing.
  6. 06

    the status quo (idiom)

    The way things currently are, especially when someone wants to keep them that way.

    In statu quo ante bellum.

Last updated August 3, 2026