Chord symbols summarize the notes behind the harmony. Understanding C, Cm, C7 and Cmaj7 makes chord sheets easier to read, transpose and correct.
Major triads
A major triad contains a root, major third and perfect fifth. C major uses C, E and G. A letter by itself normally represents a major chord.
Minor triads
A minor triad lowers the third by one semitone. Cm contains C, Eb and G. The lowercase “m” after the root indicates minor quality in common chord notation.
Dominant seventh
C7 adds a minor seventh to a major triad. Dominant sevenths often create a strong pull toward another chord, especially when functioning as V7.
Major seventh
Cmaj7 uses a major seventh. It has a different sound and function from C7, so the two labels should not be treated as interchangeable.
Extensions and suspensions
Symbols such as 9, 11, 13, add9, sus2 and sus4 add or replace chord tones. Some can be simplified for early practice, but always compare with the arrangement before removing an important color.
Context changes the sound of the same symbol
Two chords with the same name can be voiced in very different registers. A chord sheet identifies the harmonic object but does not necessarily specify the voicing heard on the record. A Cmaj7 on piano and guitar may contain the same pitch classes while sounding quite different.
When reproducing an arrangement closely, use the symbol as a starting point and choose a voicing that matches the register, bass and melody you hear.