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In music, a triad is a set of three notes that can be stacked in thirds.〔Ronald Pen, ''Introduction to Music'' (New York: McGraw-Hill, 1992), p. 81. ISBN 0-07-038068-6. "A triad is a chord consisting of three notes built on successive intervals of a third. A triad can be constructed upon any note by adding alternating notes drawn from the scale."〕 The term "harmonic triad" was coined by Johannes Lippius in his "Synopsis musicae novae" (1612). When stacked in thirds, the triad's members, from lowest pitched tone to highest, are called:〔 * the root * the third – its interval above the root being a minor third (three semitones) or a major third (four semitones) * the fifth – its interval above the third being a minor third or a major third, hence its interval above the root being a diminished fifth (six semitones), perfect fifth (seven semitones), or augmented fifth (eight semitones). Such chords are referred to as ''triadic''. Some twentieth-century theorists, notably Howard Hanson〔Howard Hanson, ''Harmonic Materials of Modern Music: Resources of the Tempered Scale'' (New York: Appleton-Century-Crofts, 1960)〕 and Carlton Gamer,〔Carlton Gamer, "Some Combinational Resources of Equal-Tempered Systems", ''Journal of Music Theory'' 11, no. 1 (Spring 1967): pp. 37, 46, 50–52.〕 expand the term to refer to any combination of three different pitches, regardless of the intervals amongst them. The word used by other theorists for this more general concept is "trichord".〔Julien Rushton, "Trichord", ''The New Grove Dictionary of Music and Musicians'', second edition, edited by Stanley Sadie and John Tyrrell (London: Macmillan Publishers, 2001).〕 Others, notably Allen Forte, use the term to refer to combinations apparently stacked of other intervals, as in "quartal triad".〔Allen Forte, ''(The Structure of Atonal Music )'' (New Haven and London: Yale University Press, 1973): ISBN 0-300-02120-8〕 In the late Renaissance, western art music shifted from more "horizontal" contrapuntal approach toward chord-progressions requiring a more "vertical" approach, thus relying more heavily on the triad as the basic building block of functional harmony. The root tone of a triad, together with the degree of the scale to which it corresponds, primarily determine a given triad's function. Secondarily, a triad's function is determined by its quality: major, minor, diminished or augmented. Three of these four kinds of triads are found in the major (or diatonic) scale. ==Construction== Triads (or any other tertian chords) are built by superimposing ''every other'' note of a diatonic scale (e.g., standard major or minor scale). For example, C–E–G spells a triad by ''skipping over'' D and F. While the interval from each note to the one above it is a third, the quality of those thirds varies depending on the quality of the triad: *''Major'' triads contain a major third and perfect fifth interval, symbolized: R 3 5 (or 0–4–7 as semitones) *''minor'' triads contain a minor third, and perfect fifth, symbolized: R ♭3 5 (or 0–3–7) *''diminished'' triads contain a minor third, and diminished fifth, symbolized: R ♭3 ♭5 (or 0–3–6) *''augmented'' triads contain a major third, and augmented fifth, symbolized: R 3 ♯5 (or 0–4–8) The above definitions spell out the interval of each note above the root. Since triads are constructed of stacked thirds, they can be alternatively defined as follows: * ''Major'' triads contain a major third with a minor third stacked above it, e.g., in the major triad C–E–G, the interval C–E is major third and E–G is a minor third. * ''minor'' triads contain a minor third with a major third stacked above it, e.g., in the minor triad A–C–E (A minor), A–C is a minor third and C–E is a major third. * ''diminished'' triads contain two minor thirds stacked, e.g., B–D–F (B dim) * ''augmented'' triads contain two major thirds stacked, e.g., D–F–A (D aug). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Triad (music)」の詳細全文を読む スポンサード リンク
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