In linguistics, a modal is an operator that is normally used to indicate some mood distinct from indicative. Some modals in English are can, could, will, would, shall, should, might, may, and must.

In philosophy, a modal is an operator usually related to possibility. The modal operators are box, which usually means necessary, and diamond, which usually means possible. They are interdefinable as follows: box P = not diamond not P; diamond P = not box not P. Computer scientists have used box and diamond to represent other concepts than possibility, such as belief. Modal logic derives in large part from C. I. Lewis, who developed various such logics; probably the most commonly-used of these is S5.

In music, modal refers to the seven modes of the standard Western major scale: ionian, dorian, phrygian, lydian, mixolydian, aeolian, locrian. The term modal is often used to describe a particular style of jazz composition in which relatively few chords are used. A soloist is then challenged to keep up a melodically interesting improvisation over the long duration of a single chord. The classic example is perhaps the first modal jazz tune: So What, composed by Miles Davis and recorded on his Kind Of Blue album.

Of, or referring to, musical modes. It rarely, however, refers to anything other than the Gregorian modes, rather than major or minor keys or any other non-western scale (i.e. enigmatic scale, diminished scale, gypsy scale).

Mo"dal (?), a. [Cf. F. modal. See Mode.]


Of or pertaining to a mode or mood; consisting in mode or form only; relating to form; having the form without the essence or reality.


2. Logic & Metaph.

Indicating, or pertaining to, some mode of conceiving existence, or of expressing thought.


© Webster 1913.

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