The concept of relative major and minor keys and scales is very useful for understanding composition and improvisation. Relatives share the same notes. Every major key has a relative minor key and every minor key has a relative major key. Every major scale has a relative minor scale and every minor scale has a relative major scale.
Here is a simple formula you can use to calculate the relatives: If you're in a major key or scale to find the relative minor simply move a minor 3rd lower (three half steps) which on the guitar or bass is 3 frets lower (to the left) for example, C is at the eight fret of the E string, if you're in the key of C major to find it's relative minor, move three frets lower which is A. A minor is the relative minor of C major, this applies to both the key and the scale. The keys and scales of C major and A minor contain the same notes, in this case, all natural notes.
Conversely, if you're in a minor key or scale, to calculate it's relative major, move up a minor 3rd. If you're in A minor, move up three frets and that gives you a C, C major in the relative major to A minor.
To reiterate in simple terms: major to relative minor = up a minor 3rd and minor to relative major = down a minor 3rd.
Tune in next week for Part 2 of this series...