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In music theory, a dominant seventh chord, or major minor seventh chord, is a chord composed of a root, major third, perfect fifth, and minor seventh. It can be also viewed as a major triad with an additional minor seventh. When using popular-music symbols, it is denoted by adding a superscript "7" after the letter designating the chord root.〔Benward & Saker (2003). ''Music: In Theory and Practice, Vol. I'', p. 77. Seventh Edition. ISBN 978-0-07-294262-0.〕 The dominant seventh is found almost as often as the dominant triad.〔Benward & Saker (2003), p. 199.〕 In Roman numerals it is represented as V7. The chord can be represented by the integer notation . Of all the seventh chords, perhaps the most important is the dominant seventh. It was the first seventh chord to appear regularly in classical music. The name comes from the fact that it occurs naturally in the seventh chord built upon the dominant (i.e., the fifth degree) of a given major diatonic scale. Take for example the C major scale (C, D, E, F, G, A, B, C): 400px The note G is the dominant degree of C major—its fifth note. When we arrange the notes of the C major scale in ascending pitch and use only these notes to build a seventh chord, and we start with G (not C), then the resulting chord contains the four notes G–B–D–F and is called G dominant seventh (G7). The note F is a minor seventh from G, and it is also called the dominant seventh with respect to G. ==Function== The function of the dominant seventh chord is to drive to or resolve to the tonic note or chord. This basic dominant seventh chord is useful to composers because it contains both a major triad and the interval of a tritone. The major triad confers a very "strong" sound. The tritone is created by the co-occurrence of the third degree and seventh degree (e.g., in the G7 chord, the acoustic distance between B and F is a tritone). In a diatonic context, the third of the chord is the leading-tone of the scale, which has a strong tendency to pull towards the tonal center, or root note, of the key (e.g., in C, the third of G7, B, is the leading tone of the key of C). The seventh of the chord acts as an upper leading-tone to the third of the scale (in C: the seventh of G7, F, is a half-step above and leads down to E).〔 This, in combination with the strength of root movement by fifth, and the natural resolution of the dominant triad to the tonic triad (e.g., from GBD to CEG in the key of C major), creates a resolution with which to end a piece or a section of a piece. Because of this original usage, it also quickly became an easy way to trick the listener's ear with a deceptive cadence. The dominant seventh may work as part of a circle progression, preceded by the supertonic. In rock and popular music songs following, "the blues harmonic pattern," IV and V are, "almost always," major minor seventh chords, or extensions, with the tonic most often being a major triad, for example Bill Haley and the Comets' "Rock Around The Clock" and Buster Brown's "Fanny Mae", while in Chuck Berry's "Back in the U.S.A." and Loggins and Messina's "Your Mama Don't Dance" the tonic is also a major minor seventh.〔Stephenson, Ken (2002). ''What to Listen for in Rock: A Stylistic Analysis'', p. 82. ISBN 978-0-300-09239-4.〕 Used mostly in the first fifteen years of the rock era and now sounding somewhat, "retrospective," (Oasis' "Roll With It") other examples of tonic dominant seventh chords include Little Richard's "Lucille", the Beatles' "I Saw Her Standing There", Nilsson's "Coconut", Jim Croce's "You Don't Mess Around With Jim", and the Drifters' "On Broadway".〔 Chuck Berry's "Rock And Roll Music" uses the dominant seventh on I, IV, and V.〔Stephenson (2002), p. 75.〕 See: Twelve-bar blues. 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「Dominant seventh chord」の詳細全文を読む スポンサード リンク
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