When it comes to playing chords there can be two approaches:
- play chords exactly based on the scale notes
- play approximated triad and seventh chords, which means you will be playing chord notes outside of the scale, while still making sure that the final sound is as you want it.
Exact chords from scale notes
If you play the diatonic chords of the major scale for songs based on the major scale, you are playing chords which have only those notes which are found in the scale.
The major scale diatonic chords are all simple major and minor triads along with one simple diminished chord triad.
The chords won't be so simple when you get beyond the major scale and its modes. Even the chords of the melodic minor scale are complex than the chords we usually see.
Mayamalavagowla scale will not give us all major and minor triads when we follow the usual method of finding chords from the scale by starting at each note and taking two more alternate notes. (the exact chords of each mode of mayamalavagowla)
You can try finding the exact chords and harmonize the melody based on chords which have only the exact scale notes with not extra additions.
But another way of making the song sound more 'popular', is to try find triads which may have two notes from the scale and the third note is not from the scale, but helps you form a triad which sounds alright with the melody phrase you have.
Of course, if the scale gives you a triad using only the notes from the scale, that is the first preference.
Two notes given, fit to nearest triad
This videos shows a malahari geetam (note positions of mayamalavagowla) being played with triads.
Hamsadhwani phrase harmonized
See this example where chords are found for a phrase of raaga hamsadhwani.
Hamsadhwani is a janya raga, and does not have all the notes of the major scale though whatever notes Hamsadhwani has are same as in the major scale.
Abhogi – chords by phrase + root
The Raaga abhogi does not have the Pa swara, the 5th note.
Raga Abhogi has the notes:
- S R2 G2 M1 D2 S
- Sa, big Ri, small Ga, small Ma, big Dha, Sa
- Root, major 2nd, minor 3rd, perfect 4th, major 6th, Root
If we add a fifth (Pa) and a minor 7th (N2 or small Ni) to the Abhogi raga or scale, we get the Kharaharapriya (the melakarta raga of which Abhogi is the janya to) or the Dorian Mode.
If i were to sing Abhogi in D, i would naturally try to use the chords of the C major scale. D dorian is the second mode of the C major scale. Modes share the same chords. So, the diatonic chords of C major scale – C, Dm, etc – will be tried on the respective swara or note of Abhogi.
You don't have the Pa and Ni notes in abhogi, but the chords corresponding to those swaras have two other notes making the chord usable over those two notes.
For example. the Pa note is A for D dorian. Am is the chord. Am has A C E notes in it. We don't have A or the Pa in D abhogi, but we can use Am on C (Ni swara) and E (Ri swara).
Am i saying it will work always? There are two more chords that are possible for each of the swaras. You need to try them. Then decide what sounds alright for you in the particular situation.
Phrase, possible chord, the root
Think of the particular phrase you have. Try the chords that will fit. The choice of chords was reduced by finding possible chords based on the root.
Restricted by the root, try the possible chords for the particular phrase you have and decide what is musical according to you for the situation.
There is the freedom and responsibility of choice, though the options can be brought down to a manageable few using theory and logic.
If not, what is the point anyway.