Function
The function of the dominant seventh chord is to drive to or resolve to the tonic note or chord.
...the demand of the V7 for resolution is, to our ears, almost inescapably compelling. The dominant seventh is, in fact, the central propulsive force in our music; it is unambiguous and unequivocal. —Goldman, (1965: 35)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. 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. See: Twelve-bar blues.
Read more about this topic: Dominant Seventh Chord
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