Why is the Ekeland variational theorem called the Ekeland variational principle?

I think (or maybe I studied somewhere) this is because of its equivalency with the Takahashi theorem, the Caristi theorem and completeness of space. But one of my colleagues believes this is because of its fundamental influence in variational analysis.

Can one help me about the history of this calling?

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    $\begingroup$ en.wikipedia.org/wiki/Variational_principle $\endgroup$
    – user139844
    Jan 4, 2022 at 17:40
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    $\begingroup$ To the extent that it is a history question, this should be on HSMSE. $\endgroup$
    – LSpice
    Jan 4, 2022 at 18:58
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    $\begingroup$ The word "Principle" in mathematics is usually applied to very general and widely used theorems with simple proofs. Examples: maximum principle, reflection principle, Phragmen-Lindelof principle, Variational principle. $\endgroup$ Jan 4, 2022 at 23:11

1 Answer 1


In this particular case the word "principle" most likely became attached to Ekeland's variational theorem because of the title of the paper where he derived it:


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