In French, when concluding a demonstration, we say "CQFD", which stands for "Ce Qu'il Fallait Démontrer" (What was to be demonstrated).

Does English have an equivalent for this ?

  • 4
    "This concludes the demonstration" is about it for a demonstration. Unless you're talking about mathematics, when you have proven a theorem. At the end of a proof, one may place "QED" from Quod Erat Demonstrandum 'That which was to be demonstrated'. Outside the "D" in Demonstrandum, however, Demonstration is not normally used in its mathematicological sense in English, outside a specificially logical or mathematical context. Which is not summoned up by use of the phrase "concluding a demonstration". Commented Sep 20, 2013 at 15:35
  • 2
    A completely language agnostic option would be to use ∎ (the tombstone mark). This is most commonly seen at the end of a proof. Commented Sep 20, 2013 at 20:55
  • CQFD in French is Ce Qu'il Faut Démontrer, placed at the end of a mathematical demonstration. But sometimes, we the french mean by CQFD : Ce Qu'il Fallait Dire = what had to be said.
    – boutonnet
    Commented Nov 9, 2016 at 23:12
  • In common language, CQFD signifies to your interlocutor that (s)he has perfectly illustrated your point and that you are in complete agreement.
    – Breiz
    Commented Mar 21, 2018 at 17:32

1 Answer 1


Q.E.D - Quod erat demonstrandum - is put at the end of of a proof to signify that what we attempted to prove has been proven.

Q.E.F. - Quod erat faciendum - is a term that is used in geometric proof to signify that the geometric construction has been completed. It is a rarely used English abbreviation.

From the article the correct translation is Q.E.F. but from your description Q.E.D. sounds more accurate because it comes at the end of a proof/demonstration.

Note: From the comments below CQFD is always equivalent to QED.


Not the answer you're looking for? Browse other questions tagged or ask your own question.