A central concept in music theory is voice-leading. For example, in the transition from a C major triad in the root position (C-E-G) to an F major triad in the second inversion (C-F-A) the voice-leading is obvious: the E moves up a minor second to F, and the G moves up a major second to A. The concept of voice-leading is valuable for understanding chord progressions and transpositions from key to key.
I have been learning Telemann flute duets, the six sonatas, TVW 40, which are essentially exercises in two-part counterpoint. There is plenty of voice-leading, as, for example, Telemann adds a G# to a run, leading to an A, and signalling that he has modulated from the key of D to the key of A. But I wonder whether Telemann was thinking in terms of what we now know as classical Western harmony.
There are plenty of arpeggios in these duets, spelling out chords, and they lead from one measure to the next, but I find myself wondering, as I play them, whether Telemann thought of them as chords. By contrast, if you look at the lead sheet of a jazz standard, you'll see a melody line, written in the treble clef, with the names of chords written above it. The musicians who play the piece use the chords as indications of how the melody should be accompanied and as the basis for improvisation. To fit the improvisation over the chord progression, or to play a walking bass line, you have to know what the notes of the chords are and what scale they suggest. Most of the time, this isn't an insuperable challenge. To take a slightly uncommon example, when you see a chord labelled C7#5, you have to understand that the chord notes are C-E-G#-Bb (=A#), which implies a whole tone scale: C-D-E-F#-G#-A#-C. My question is the following: is a C7#5 really a chord? Those four notes do not appear together in any ordinary diatonic scale. Similarly, a very common chord in jazz is written as a six, as in C6 (C-E-G-A), but it's really an A minor seventh in the first inversion. If it really is anything.
When did Western European composers begin to think of their music as based on progressions of chords? By the baroque period, composers were definitely thinking in terms of keys. The fourth Telemann sonata is clearly and intentionally in the key of b-minor, though one of the movements is in the relative major, D. But Telemann never stays for very long in the nominal key, and he uses voice-leading to move from key to key. A passage in F#7 is followed by a passage in b-minor, as classical harmony tells us that it should. But how did Telemann conceptualize it?
The name of a chord designates a certain collection of notes. A musicologist looking at a score sees an array of notes and labels it as a chord. In a sequence of chords, a chord progression, one chord leads to another. But the reason why the arrays of notes move forward is undeniably the voice-leading, the movement from the notes in one chord to those in the following chord.
In jazz harmony, people talk about tension - the tension created by a dissonance such as the minor second (or major seventh) between B and C in a C major 7 chord - and the release of tension in consonance. The tritone (augmented fourth or diminished fifth) in a dominant seventh chord (e.g. B and F in a G7 chord) is resolved into a major chord - in Western classical music, in rock and roll, in popular music, and in jazz.
That, dear readers, is a matter of voice leading, which underlies harmony.
