I recently had a conversation with someone about music for a single line instrument such as a flute. Their argument was that because only one note could be played at any one time, there was no harmony in the music, nor could their be as the flute, or indeed any wind instrument, was unable to play harmonies.
This is incorrect, in my view. A scale can be used both for melodic and harmonic reasons. The fact that the notes occur in a sequential order is beside the point.
For example, in the key of C Major, the scale of A Harmonic minor is introduced with a G#, that is the only difference. Although no other note is played at the same time, the G# implies E7 which is the dominant chord that creates the perfect cadence to A minor. So G# creates the harmony of E7, and in this case E7b9 (mode V of A Harmonic minor E Phrygian Major 1 b2 3 4 5 b6 b7) which then resolves to the key of A minor.
Now, if the music then introduces D# after the G# before the resolution to A minor, the scale is A Hungarian minor (A B C D# E F G#). The harmony created by the D# is B7, or B13b5b9 to be precise, and this dominant chord resolves to E7. So the inclusion of A Hungarian minor is creating a V-V-i in A minor. All with scales, no double stops, chords or anything else. The fact is that some scales are only ever used for harmonic purposes, whether the notes are played simultaneously or not.
Here is another example. Neapolitan minor. Not used much, certainly not nowadays. But in C Major, the alteration of D to D# creates E Neapolitan minor (E F G A B C D#). The D# is the 3rd in B7b9 and resolves to E minor (the full dominant chord is B7b5b9b13). Again, no chords were harmed in this theoretical exercise. Scales used for harmonic reasons, try it and see.