Piano World Home Page Forums Our Most Popular Forums Adult Beginners Forum Do chord substitutions need to be diatonic to the key

E.g. I-IV-V in C major

I want to substitute the G dominant with a B flat chord let's say.
Or the F with an A major chord of some sort.

The short answer is 'anything goes' if it sounds ok and suits the genre. If you're going to substitute Bb major for the IV, IOW you're making Bb major the passing chord to the V, that can sound really good. But Bb is already outside C diatonic?

You can also substitute Bb for the G if you have a melody which makes sense with that movement.

Thank you

The traditional view of the replacement of the dominant in natural Major:
V , III m ,VII dim


in melodic Major:
Vm
VII b



In jazz:
V7
IIb7
Vii 7
According to the chromatic system of B. Bartok can build dominant chords
on steps of diminished seventh chord - in this case: G, Bb, Db, E; wherein the chords can be both major and minor.

Everything's possible. It's all depends on what you feel you wish to achieve. It's music and music is art. It is not a mathematical equation. In C, substituting G with Bb sounds to me like a transition to F whereas substitution F with A would be transition to DMaj etc. because C is a dominant to F and playing C-Bb would give me idea to resolve in F. On the other hand A is a dominant to D. You see. That's what I, myself, imagine based on what you have written. You may have totally different concept
My teacher says there's no rules and if there are, you break them :p

Those are my thoughts, exactly. The downside is that 'any old thing' might not sound attractive although it's sometimes possible to rationalise or soften-up an outlandish harmony or chord sequence with a suitable melody.