It is not about modal practice/playing in this instance
You can start your melody on any note and you can start your counter-melody on any note that is consonant or dissonant - the effect and perception comes back to how you treat consonance and dissonance in your writing
You can start a melody on any degree of the scale
- a common pickup beat start (beat 4 or the and-of-4)) is to begin on the dominant or leading tone and progress to the tonic e.g in C this would be G/C or B/C (/ indicates move up to) both of these assume that we start on chord V and proceed to chord I
- you can start on the 3rd and come down to the tonic, e.g. E\C; or move up to the tonic, e.g. E/C (this is a partial arpeggio of chord I)
- you can start on the 5th and move down through 3 to the tonic, e.g. G\E\C (this is a full arpeggio of chord I); or up by step to the tonic, e.g. G/A/B/C (this is a scale run)
- you can start on any note that matches your underlying chord at that point or is even a non-chord tone (greater tension) that moves to a chord tone
Writing counter melody lines means using the principles of harmony to select key points for harmonic convergence (notes from the chord for both parts) and allowing for harmonic divergence
- 1 note may be from the chord the other is a note a scale step away from a chord note,
- in some instances both notes will not be part of the chord
- this is normal melodic and counter-melodic writing practice