Popular harmony
Musicians use various kinds of chord names and symbols in different contexts, to represent musical chords. In most genres of popular music, including jazz, pop, and rock, a chord name and the corresponding symbol are typically composed of one or more of the following parts:
For instance, the name C augmented seventh, and the corresponding symbol Caug7, or C+7, are both composed of parts 1, 2, and 3.
Except for the root, these parts do not refer to the notes that form the chord, but to the intervals they form with respect to the root note. For instance, Caug7 indicates a chord formed by the notes C–E–G♯–B♭. The three parts of the symbol (C, aug, and 7) refer to the root C, the augmented (fifth) interval from C to G♯, and the (minor) seventh interval from C to B♭. A set of decoding rules is applied to deduce the missing information.
Although they are used occasionally in classical music, typically in an educational setting for harmonic analysis, these names and symbols are "universally used in jazz and popular music", in lead sheets, fake books, and chord charts, to specify the chords that make up the chord progression of a song or other piece of music. A typical sequence of a jazz or rock song in the key of C major might indicate a chord progression such as "C – Am – Dm – G7".
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