Function label
Symbol for the harmonic function (T, S, D).
What it means
The function label is the sign with which analysis records which role a chord plays in its key. It does not ask on which note a chord is built but what it serves for: whether it is a point of rest, whether it leads toward this point of rest, or whether it leads away from it. Three principal functions suffice for this — tonic (I), subdominant (IV), and dominant (V). All other sonorities are described as variations or substitutes of these three.
In the notation
It is written with letters below the staff or below the bass line: T for the tonic, S for the subdominant, D for the dominant. Capital letters stand for major sonorities, lowercase letters for minor ones. Appended signs extend the indication: a raised p designates the relative, a g the mediant, an appended 7 the added seventh, as in D7. A bracket or an arrow indicates that a sonority relates to a degree other than the tonic — this is how the secondary dominant is notated. A crossed-out label stands for the deceptive cadence, in which the expected resolution fails to appear. In addition the degree can be added in Roman numerals in brackets.
Musical use
The gain of this system lies in the fact that it makes connections visible across different keys: a cadence T–S–D–T looks the same in every key, and a modulation can be described as a change of the frame of reference. It is especially suited to music that is clearly tonally bound. Where this tie is missing — in modal music, in large parts of the twentieth century — it reaches limits, and the degree label or a purely descriptive analysis leads further.
The function label is to be distinguished from figured-bass figuring: the latter says which intervals are to be played above the bass, the former what meaning the sonority has in the whole.
Performance practice
When working up a piece, write the functions in pencil below the bass line — even the first bars then reveal what the music is heading for. Do not analyse chord by chord but look first for the cadences and work backward from there. Within a piece, stay with one system instead of switching between functions and degrees.