Common tone

Tonic and tonic parallel in C major: two common tones  Play .

In music, a common tone is a pitch class that is a member of, or common to two or more entities. For example, a note shared between two chords in a chord progression. Common tones are a consideration in voice leading.

Diatonic set theory

C is a common tone between the C and G major scales, as are D, E, G, A, and B.

A common tone is a pitch class that is a member of, or common to, a musical scale and a transposition of that scale, as in modulation (Johnson 2003, p. 42). Six of seven possible common tones are shared by closely related keys, though keys may also be thought of as more or less closely related according to their number of common tones.

Common tones between G major and C major and between C major and F♯ major, 6 and 2 common tones respectively.

In diatonic set theory the common tone theorem explains that scales possessing the deep scale property share a different number of common tones for every different transposition of the scale. However many times an interval class occurs in a diatonic scale is the number of tones common both to the original scale and a scale transposed by that particular interval class. For example, then, modulation to the dominant (transposition by a perfect fifth) includes six common tones between the keys as there are six perfect fifths in a diatonic scale, while transposition by the tritone includes only two common tones (for indeed there are two tritone intervals in a diatonic scale) (Johnson 2003, p. 42).

Diatonic scale transposed a perfect fifth: since it contains six perfect fifths the two scales a perfect fifth apart have six common tones.

See also

• Approach chord
• Voice leading
• Walkdown

Sources

• Johnson, Timothy A. (2003). Foundations of Diatonic Theory: A Mathematically Based Approach to Music Fundamentals. Mathematics Across the Curriculum. Emeryville, CA: Key College Publishing. ISBN 978-1-930190-80-1. LCCN 2002075736. 

Musical set theory
All-interval tetrachord Complement Forte number Identity Interval class Interval vector Multiplication Permutation Pitch class Pitch interval Pitch-interval class Set List Similarity relation Transformation Z-relation
Diatonic set theory	Bisector Cardinality equals variety Common tone Diatonic scale Deep scale property Generated collection Generic interval Maximal evenness Myhill's property Rothenberg propriety Specific interval Structure implies multiplicity