Leading-tone exchange chord
A chord formed by shifting the root of a major triad down a semitone, or the fifth of a minor triad up a semitone (C major → E minor).
What it means
The leading-tone exchange chord is a concept from the function theory developed by Hugo Riemann. It describes a chord derived from the tonic triad by shifting a single note by a semitone: in major the root moves down a semitone, in minor the fifth moves up a semitone.
In C major, the tonic C–E–G thus becomes E–G–B, the E minor triad. In A minor, A–C–E becomes A–C–F sharp, the F major triad. The leading-tone exchange chord shares two of its three notes with the tonic and so counts as one of its closest related chords.
Musical use
In German function theory the leading-tone exchange chord is labelled Tl (in major) or tG (in minor) and, alongside the relative and the counter-relative chord, is treated as one of the third-related substitutes for the tonic. It appears above all in deceptive-cadence-like turns and in late-Romantic harmony, where third-related chords replace classical cadential progressions.
It should be distinguished from the plain relative chord, which shares two notes with the tonic while the third moves by a full third, and from the counter-relative chord, which also shares two notes with the tonic but differs on the other side.
Performance practice
Play the tonic and the leading-tone exchange chord one after the other and listen specifically for the single note that changes. This trains your ear for the close relationships between third-related chords, a hearing skill often needed when analysing late-Romantic music.