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- "Tertial" redirects here. For the feathers in a bird's wing see tertials. For the disease formerly known as tertian fever see Malaria.
In music theory, tertian (Latin: tertianus, "of or concerning thirds") describes any piece, chord, counterpoint etc. constructed from the interval of a (major or minor) third. An interval such as that between the notes A and C encompasses 3 semitone intervals (A-B♭-B♮-C) and is termed a minor third while one such as that between C and E encompasses 4 semitones (C-D♭-D♮-E♭-E♮) and is called a major third (See Major and minor).
A common triad chord can be regarded as consisting of a "stack" of two such intervals. A musical scale may also be analysed as a succession of thirds (See Ladder of thirds). The meantone temperament, a system of tuning that emphasises pure thirds, may be called "tertian".
Chords built from sixths may also be referred to as tertian because an ascending sixth is equal to a descending third and vice versa: any sixth can be taken as the inversion of a third. For instance the interval C-A is a major sixth that, when inverted, gives the interval A-C, which is a minor third.
- Benward & Saker (2009). Music in Theory and Practice, Vol. II, p.370. ISBN 978-0-07-310188-0. "Tertian (third based) harmony".
- Benward & Saker (2009), p.279.