Finding out which scales contain a specific chord

Question

Notation note: scales will be notated as C Major, D minor, etc. and chords as Am, F, etc.

Once you know a scale, yo know which chords it contains, for example the C Major scale contains the chords:

C, Dm, Em, F, G, Am, Bdim

But what about finding out which scales contains a specific chord, without of course going through all the scales and seeing if the specific chord is in them.

For example, which scales contain the chord C?

I thought about using the fact that I know the degrees of the major an minor keys:

M : I, ii, iii, IV, V , vi, vii*

m: i, ii*,III, iv, v , VI, VII

So I was able to find out that the C chord is in the following scales:

C Major, G Major, F Major, A minor, E minor, D minor.

But when I tried to use this method of the B chord thing did not go as well...

Answer 1

You've actually found the answer. For the C Major chord, start with the C Major scale and select I, IV, and V (C, F, and G); those are your major scales containing C Major. Then take each of their relative minors (down three half-steps): A, D, and E.

The same thing works for B Major — B Major, E Major, and F# Major plus G# minor, C# minor, and D# minor all contain the B Major chord.

Alternatively, you can think of this in terms of the circle of fifths. C Major and A minor, plus their immediate neighbors on the circle, all contain the C Major chord. This is true for any other chord/key and its relative minor plus their neighbors.