In music theory, the tonic parallel (relative chord, German: Parallelklang) is a diatonic function and chord, relative to the tonic, and thus considered to have or fulfill the function of the tonic. The term is used in German theory and derives from the work of Hugo Riemann. It is abbreviated "Tp" in major and "tP" in minor.
Dr. Riemann...sets himself to demonstrate that every chord within the key-system has, and must have, either a Tonic, Dominant or Subdominant function or significance. For example, the secondary triad on the sixth degree [submediant] of the scale of C major, a-c-e, or rather c-e-a, is a Tonic 'parallel,' and has a Tonic significance, because the chord represents the C major 'klang,' into which the foreign note a is introduced. This, as we have seen, is the explanation which Helmholtz has given of this minor chord."
In C major:
- Tp is A-minor, US submediant
In C minor:
- tP is Eb-major, US mediant