mediant

The mediant is scale degree 3 of a key: the pitch a major third above the tonic (in a major key) or a minor third above the tonic (in a minor key), and the bearer of the mediant function — the degree that occupies the middle position of the diatonic scale and divides the perfect fifth. In C major the mediant is E (the root of the iii chord, a minor triad), and in A minor the mediant is C (the root of the III chord, a major triad). PARAMETERS: (1) intervallic status — the mediant sits a major third above the tonic in major keys and a minor third above the tonic in minor keys; it divides the perfect fifth (tonic to dominant) into two thirds, making it the harmonic midpoint of the diatonic fifth; (2) functional role — it is the degree that commonly functions as a weak pre-dominant (moving to the dominant as iii–V or to the tonic as iii–I); the mediant triad (iii) is a standard pivot chord, sharing two tones with both the tonic triad and the dominant triad (in C major: I = C-E-G and iii = E-G-B share E and G; iii = E-G-B and V = G-B-D share G and B) — it is the chord, not the pitch, that links I and V, and the shared tone of the I and V triads themselves is G, the fifth degree, not the mediant; (3) relational definition — the mediant is defined relative to the tonic (the mediant of C major is E; of A minor is C) and is the third ordinal of the key's scale. PERSISTENCE: codified in Western tonal and harmonic theory, taught in music-theory and harmony curricula (scale-degree numbering; Roman-numeral analysis naming iii in major and III in minor), reproduced in composition and analysis practice (identifying the mediant's pre-dominant and pivot roles in voice-leading and modulation), and maintained through the conventions of tonal notation. Distinctions: from the supertonic (scale degree 2 — a second above the tonic, the first degree of departure; the mediant occupies the third ordinal slot); from the subdominant (scale degree 4 — a fourth above the tonic, the degree of departure; the mediant is below the subdominant); from the dominant (scale degree 5 — the point of tension; the mediant sits a third below it and carries a subordinate role); from a bare pitch (any point on the pitch axis; the mediant is a pitch bearing the specific third-degree status and the middle-function); from the iii chord (the triad built on the third degree — a chord built ON the mediant, not the degree and function itself). [formal: medius | substrate: mind | horizon: centuries | explicit: yes | epoch: 0.01]