Common tone (chord)

In music, a common tone is a pitch class that is a member of, or common to (shared by) two or more chords or sets). For example, a note shared between two chords in a chord progression. Common tones are a consideration in voice leading and voicing. For example, common tones between chords may influence the inversions used, with common tones often "preserved" or "retained", as this is in agreement with voice leading principles such as smoothest and least possible movement. "The note...contained in both chords is called the common tone" (Diller 1921, p. 87). A common tone is a, "tone shared by both triads" (Benward & Saker 2003, p. 162).

Any tone contained in two successive chords is a common tone. Chords written upon two consecutive degrees of the [diatonic] scale can have no tones in common. All other chords [in the diatonic scale] have common tones. Common tones are also called connecting tones, and in part-writing, are to be retained in the same voice. Chords which are four or five degrees apart have one common tone. Chords which are three or six degrees apart have two common tones. Chords which are one or seven degrees apart have no tone in common. (Woodruff 1899, p. 61)

Abbé Vogler (1749–1814), Weber (1779–1839), Hauptmann (1792–1868), A. B. Marx (1795–1866), and earlier theorists have emphasized, "common-tone retention and smooth voice leading in...[their] treatment[s] of harmonic succession [chord progressions]" (Engebretson 2008, p. 109). It may be considered a guideline or a rule (Klauser 1890, p. 202).

Common-tone diminished seventh chords resolve to a chord whose root is common to both chords (♯ii^o resolves to I⁶, in C: D# F A C resolves to C E G).

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