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THE DOMINANT SEVENTH CHORD 121
THE DOMINANT SEVENTH CHORD The Seventh may be added to the Dominant Chord. As an example, take G-B-D,
the Dominant Chord in C Major, and add to it F (the Seventh), thus:
Up to this point we have been working with Triads, or Three-Tone Chords, in which we had to double a Member in order to give a Four-Part Harmony, but the addition of the Seventh to the Dominant Chord gives us a complete Four-Tone Chord. It is known as the Dominant Seventh Chord. This Chord is one of the most important, and most used, Chords in all Music. It lies at the very foundation of all so-called Dissonant Harmony.
By a Dissonant Interval we mean one which does not appear to be satisfactory standing by itself, but which appears to lean upon some other Interval. Take this very Interval about which we have been talking: the Seventh (a Minor Seventh, by the
way). Strike it by itself, and listen: It seems to need something
to follow. Now strike it again, and allow the Seventh (F) to de-trend One Degree (to E orand the ear is satisfied, thus: This
motion of a Dissonant Member of a Chord is called its Resolution. Consonant Intervals, Thirds, Fifths, Sixths and Octaves, such as we have been using up to this point, are satisfactory in themselves and do not require Resolution.
Since the Seventh requires Resolution, it stands to reason that whichever Chord follows the Dominant Seventh Chord must contain that Tone upon which the Seventh resolves. In our example we found F (the Seventh) resolving upon E or Eb. Now we know E to be the Third of the Tonic Chord of C Major (C-E-G), and E^ to be the Third of the Tonic Chord of C Minor. We also know, from our study of the Cadences that the Tonic is the most likely Chord with which to follow the Dominant. Let us see how the several parts or voices will move.
We know already that the Seventh is to descend: The Thlrd
of the Dominant 'Seventh Chord, being the Leading Note in the Scale always has an upward tendency: This leaves the Fifth of the Chord