Recently I was listening to the great film composer Nino Rota’s music from The Godfather movies. I noticed how, in his melodies, he did something that John Lennon was also very good at – taking a melody that was basically diatonic (all in one scale) and mixing in a note from outside the scale to give the melody more bite and flavor.
(I encourage you to give the examples mentioned here a close listen, keeping in mind the points raised.)
It’s common in most folk- and blues-based melodies (which includes most pop music) to have melodies that are all or mostly diatonic. For example, in Rota’s Godfather Theme, the ‘A’ Section of which is 8 bars long and in C minor, he uses the ‘Natural Minor’ scale (the same as a major scale, but it starts on the 6th tone instead of the root) – in this case C-D-Eb-F-G-Ab-Bb-C. However, at two crucial points, at the end of bars 5 and 7, he substitutes a B Natural for a f. This gives the melody a lot more color than if he had stayed in the same scale all the way through.
Very similarly, in Girl by The Beatles, John Lennon uses the same Natural Minor scale in C minor and he also, in bars 3 and 7 of the “A’ Section, substitutes B Natural for Bb, to similar great effect.
Even in Rodgers and Hammerstein’s Do Re Mi, a song that’s literally about singing a major scale, Richard Rodgers augments (raises) the 4th when he gets to ‘La’, the 6th degree of the scale. And then when he gets to ‘Ti’ (the 7th degree), he ups the ante by raising the 5th scale tone. (In The Sound Of Music, the song is sung in the key of Bb and is based on a Bb major scale, so that means he raises the Eb to an E and then the F to an F#). But naturally he then goes back to the major scale and brings-it-back-to-Do Do Do Do-DO!!
Most of us tend to write our melodies in one scale, at least for a particular section of a song. The idea here is really about creating a tonality in the first part of the melody by using a particular scale, and then subverting the natural expectation that the same tonality will continue by introducing a note from outside the scale. This is something really worth fooling around with when writing melodies.
So, after you’ve established a tonality in the first few bars of your melody, try moving one of the notes up or down by a half step. The results might be a pleasant surprise.