The use of chords extensions in classical music is different from that in pop & jazz. In the classical notation, extensions are dependent on the key. Thus, C7
could mean a chord with a major seventh, if it is in the key of C major. Thus the seventh is indicating the seventh tone in the scale, counting from the note c. In the key of F major however, C7
will denotate a chord with a minor seventh, because the note b flat is part of the scale.
In pop and jazz however extensions are independent of the key. In those styles, a 7
will always indicate a chord with a minor seventh. A major seventh is always denoted by maj7
or ^
or something similar, but never by 7
.
Musicians should therefore be aware of each other's theoretical background. Unfortunately, the differences in notation between classical music and pop and rock are too large to ever hope for a unification in the chord language. These differences become even larger when chords are analyzed in roman numerals (also called scale degrees). We'll get to that subject in a later post.