The Prelude to Tristan and Isolde is one that became extremely popular for one main reason: the invention of what has become known as the Tristan Chord. The Tristan Chord was born out of Wagner's desire to prolong the feeling of grief, the feeling of sorrow.
The Tristan Chord is found in m. 2 - f, b, d#, g # this becomes a significant chord for most of the prelude.
The prelude I believe has three main motives. The first begins in measure 1. For purpose sake it is in the alto voice through until m. 3. The second motive begins in the soprano voice til m. 3. Motive c can be be found in m. 16 & 17. It is evolved from b. The difference lies in that in c - the third note has been lengthened.
The piece is primarily in a minor. Again we have the initial motives from m. 1 - 3 - followed by the same motive but up a m. 3 in 4 -7. This occurs later in mm. 8 - 11 and then follows in 12 - 13 but an octave higher.
The Tristan Chords that I found are as follows: m. 2 / 40 / 102 - 103 / 106 - 111. (the 106 - 111 is a Tristan Chord broken up in the cellos)
The hard thing about this piece is the tension - there are not a lot of perfect authentic cadences. We have a V - VI cadence in mm. 16 - 17. An imperfect cadence in mm. 44 & 74. At m. 42 we have a key change to what I believe is F# minor. Then at m. 71 back to a minor.
Measures 74 - 80 serves as an extension / development of the material from 63 - 74.
I am not sure what else to say - what was everyone else's findings? I was a little confused to what actual form / key this is in? does anyone have any ideas?