In counterpoint pedagogy harmonic dissonance and consonance is taught with one note as the "Cantus Firmus" against one or more other notes. How does this knowledge of consonance or dissonance apply when the melody is played over a chord? For example, the 6th is a consonance in CP but over a triad, wouldn't the 6th be considered dissonant and need to resolve? A 7th would also be dissonant in CP but if your chord was a 7 chord? Or what about if you accent a minor second or 9th? This sounds great against a sus 2 or sus4 chord where the 3rd is not present.
The problem in your question is you are combining two different standards of dissonance.
It isn't a problem of combining counterpoint with styles other than Bach or Palestrina generally. But you specifically have to rethink the treatment of dissonance in traditional counterpoint.
Probably the easiest example to look at is the harmonic seventh. Traditionally, it's a dissonance you should resolve. But in modern harmony a seventh is a bit mixed, sometimes treated like a dissonance, but also can be considered a consonance, a tone that absolutely does not need to be resolved.
If you bring in seventh and ninth chords along with
add6/thirteenth chords, you pretty much can discard all the rules of dissonance handling from traditional counterpoint. You literally end up with no dissonant diatonic tones except for the fourth/eleventh which tends to be a dissonance until the harmonic style moves into quartal or quasi-quartal harmony.
But discarding dissonance rules, or at least loosening them, does not leave you with nothing. Counterpoint study will still provide a lot:
- the obvious one is relative motion, developing a melodic contour that contrasts from the chord's voice leading and the bass.
- balanced voicing, make sure all tones of chords are played
- a sense of stability/instability regarding chord inversions
- probably the real deep level understanding from counterpoint will be that chords are the result of voice movement, if you really get that, you will probably stop thinking of chord progressions with melodies added on top which homophony rather than counterpoint
- from the voice leading and chord inversion perspective, the bass should become truly melodic rather than roots and fifths with passing tones, the bass can accent chordal thirds, fifths, and sevenths on strong beats and those instabilities then resolve melodically to stable voicings
- a better sense that rhythm is just as important as pitch to creating a melody and contrasting two melodies, notice how species counterpoint has categories
4:1, etc. which are rhythmic (or rather linked rhythmic/pitch) categories
- a sense of contrapuntal texture, sort of like the earlier point about homophony, contrapuntal thinking will move away from chords plus melody, that is homophonic texture, contrapuntal texture won't have two separate layers of chord plus melody, it tries to make four equal parts, the rhythm/pitch activity in
4:1will be worked into all voices
You might listen to stuff like The Swingle Singers, Lambert, Hendricks and Ross, or Chanticleer - all vocal groups that have works with modern harmony, but contrapuntal treatment to highlight all their amazing singers. Debussy's and Ravel's string quartets might be good too. The textures may be more on the homophonic side, but quartet writing also tends to highlight all four instruments so it balances homophony and counterpoint. And those quartets use a lot of seventh an ninth chords.
A good voicing of seventh chords is resolving the leading tones that it is congruent with the counterpoint rules. Ninth chords in Jazz and Pop are often resolving to the octave or upwards the 3rd (dezime).
You have more liberty to write an interesting counterpoint (already Bach was much more independent of the strict rules written by Fux), there are much more dissonances possible than we may think.
It is most important that the lines are more distant. Try it out. Write a moving bass line in contrary movement to the leading melody (cantus firmus) and use the model of imitation in the middle voices, using passing tones, changing notes and chromatic approaches. Don’t care too much about consonance, when playing above chords there will be enough of this.