Relative Keys
if you compare the A minor "pure" minor scale with the C major scale you will notice that they contain the same notes (except starting on a different note). Because of this, these two scales are referred to as "relatives"; A minor is the relative minor of C major and vice versa.
The harmonic and melodic minor scale variations are also relatives of the same major scale, e.g., A harmonic and A melodic minor are relatives of C major.
For every major scale (and ever major chord) there is a relative minor scale which is based upon the 6th note of the major scale. This is outlined in the table.
Both the major and the relative minor share the same key signature, as illustrated in these examples:
The sharpened 7th note that occurs in the relative minor key is never included as part of the key signature. Because each major and relative minor share the same key signature, you will need to know how to distinguish between the two keys. For example, if given a piece with the key signature of F# thus:
It could indicate either the key of G major or its relative, E minor. The most accurate way of determining the key is to look through the melody for the sharpened 7th note of the E minor scale (D#). The presence of this note will indicate the minor key. If the 7th note is present, but not sharpened, then the key is more likely to be the relative major (i.e., D natural notes would suggest the key of G major).
Another method is to look at the first and last chords of the progression. These chords usually (but not always) indicate the key of the piece. If the piece starts and/or finishes with Em chords then the key is more likely to be E minor.
