In music theory, the concept of root denotes the idea that a chord could be represented and named by one of its notes. It is linked to harmonic thinking, that is, to the idea that vertical aggregates of notes form a single unit, a chord. It is in this sense that one can speak of a "C chord", or a "chord on C", a chord built from C and of which C is the root. The root needs not be the bass note of the chord: the concept of root is linked to that of the inversion of chords, itself deriving from the notion of invertible counterpoint.