Derived from the Latin comparatives maior and menor, meaning greater and lesser, the terms major and minor have three separate but closely related uses: they are used (i) to specify the size of certain intervals; (ii) to specify information about a scale; and (iii) to specify information about a piece’s key.
In the first use, some intervals—seconds, thirds, sixths, and sevenths—can be further specified as major or minor. For example, one uses terms “major third” and “minor third” to denote the specific size of the generic interval of a third. In the example below, we see two pairs of thirds (so named because the second note is two steps away from the first, meaning that one has arrived at the third note). The first pair, C-E, is called a major third and comprises four half steps. In the second pair, C-E-flat, the top note has been lowered by one half step, and is thus identified as a minor third.
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Some intervals—specifically the unison, fourth, fifth, and octave—do not receive the designation major or minor.
The second and third uses of major and minor provide a basic distinction between the two most commonly used scales, and in turn, to the two kinds of keys available in Western music. A piece is said to be in a major key when the notes it most frequently uses belong to some major scale. Similarly, a piece that uses notes predominantly taken from some minor scale is usually said to be in a minor key. For additional information, consult the entries for scale and key.