by Gary Ewer, from “The Essential Secrets of Songwriting” website:
Like most songwriters, you’re probably looking for ways to look at melody construction. One aspect of melody-writing that we don’t think that much about is what it sounds like in the opposite mode. Here’s what I mean by that.
Let’s say that your melody is in the key of G major. This means that the note G is the tonic note, and the chord G, being the tonic chord, is acting as a “home” chord. The melody you’ve written will use the notes of the G major scale: G A B C D E F#
If you’re bored with your melody but don’t know why, and if you’re looking for a way to make your melody distinctive, you’ll find it really interesting to consider performing your melody in the minor key: Gm
The easiest way to do this is to change the note B to Bb, since that note is the 3rd of the scale, and is generally responsible for making a key feel major or minor. You’ll also want to change E to Eb. To make this simple, take the chords that exist in the key of G major and change them to the ones you’d find in G minor, and adjust the melody to match.
The chords of G major are: G Am Bm C D Em F#dim
The chords of G minor are: Gm Adim Bb Cm D Eb F
The first four bars of the following melody are in G major. Then, it changes to G minor. Notice the difference in mood this creates. (Sorry for the cheesy MIDI file! But it demonstrates the concept):
Changing your song from major to minor (or vice versa) is a great way to create a completely new feel for your song, and is very useful if the melody you’ve written just doesn’t do it for you.