symbols/codepoints for necessity and possibility in modal logic

From: Stephan Stiller <>
Date: Thu, 18 Jul 2013 20:27:52 -0700

Hi all,

Modal logic uses a "box" and a "diamond" (this is how they're informally
called) as operators (accepting one formula and returning another) to
denote necessity and possibility, resp. Older texts might use the
letters L and M (resp). Which Unicode codepoints do modal box and
diamond correspond to?

According to the charts, it seems like the box is
     ◻ (U+25FB)
(is this definitive?), but what about the diamond? Unlike what one might
glean from the charts, ⟠ (U+27E0) is afaiu /not/ normally used to denote
possibility in the default† sense. Wiki's "List of logic symbols"
article has something to say about this too, but I'm always cautious
about information from there.


    † eg in the sense of "λ𝑥 . ¬◻¬𝑥" with ◻ as used in say the axiom
    schema conventionally named *T* in modal logic
Received on Thu Jul 18 2013 - 22:30:04 CDT

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