When writing a melody, is the scale used determined by the current chord playing (in the chord progression) or by the song's key as a whole?

Question

This is an embarrassingly basic question, but it's been in the back of my mind for a while, and I haven't been able to find an answer.

I've been studying very basic music theory lately and trying to write some simple songs. My process is to do these three things in order:

1. Write the percussion
2. Come up with a chord progression and lay that out
3. With another instrument, write a melody on top of it all

My question deals specifically with part 3. As I understand it, a "scale" just means a palette of notes from which to choose when writing out the melody (please correct me if that's an oversimplification).

My question is this: does the scale change each time a chord changes in the chord progression (i.e., should I be choosing from different notes each time the chord changes)? Or should I be sticking with one scale that's determined by the overall key of the song?

I had assumed the former, and for example would be writing the melody in D major for the part where a D major chord was playing, and then using a different scale when the chord changed, but I'm starting to think my assumption was built on a misunderstanding.

Answer 1

If you were following the most common simple way that's taught to people just beginning learning theory, you'd be aware of the key you're in (and the corresponding scale you're using) in step 2, and you'd be using chords from that key. So for example, if in step 2 you're in D major, the most common 'beginner' technique would be to use simple triads from the D major scale, giving you the following chords to choose from:

• I – D major
• ii – E minor
• iii – F# minor
• IV – G major
• V – A major
• vi – B minor
• vii – C# diminished

In step 3, you'd also use notes from the D major scale for your melody (through the whole song), in a way that works well with the chords you're using. You might try to choose the melody notes to often follow the chord tones (the notes in the chord that you're playing at the time) on the important notes (that fall on the strong beats).

BUT... that's only one very simple way to write a song. It's definitely not "the rule", in the sense that you have to follow it - there are no rules that you have to follow. And there are songs where the harmony and melody seem to at least partly work like the other way you described - where it seems like the scale for the melody can potentially change on each chord change. There are also songs where the chords don't entirely fit into a single key, melodies that basically follow a scale but use the odd note from outside the scale, and all sorts of other patterns. And not all ways of looking at harmony require you to think of the chords and the melody separately.

Try using both ways, and see what happens - if you find one way sounds great to you and the other is terrible, then you have your answer. If you find some merit in both ways, then you are free to combine them. If you find neither way works, then have a look at some songs you do like and see what they do.

Answer 2

Most of the songs I write start with a chord progression as well. I may have a beginning melody in my head but then I will determine a chord progression before fine tuning the melody. Then I choose melody notes that harmonize well with my chord progression.

If you stick with chords that fit within the key you are writing in, then all the notes of the chords will be in the key of the song and will be found in the diatonic scale based on that key. So if you are writing in the key of C major, and stick with the basic common C major based chords, the notes you choose for the melody will all be one of the notes in the C major scale.

But certain notes will usually harmonize better with certain chords. Although there can be exceptions to this depending on where you are going with the melody and what you are trying to convey.

For a detailed discussion of the easiest way to find the notes that harmonize best with certain chords when writing your melody based on a chord progression -read this on Stack Exchange: Easy way to choose notes that go with chords

You will also find several answers to the question linked below (on Stack Exchange) that will help with your understanding of how chords and scales fit together:

How to make a song with chords and scales

Also - the following question on Stack Exchange explores situations where composers choose chords (and possibly notes) from outside the key as part of a chord progression:

Will a song written in a key only use chords from that key?

As you can see, your question comes up often in one form or another.

Have fun with your composing and writing.

Answer 3

If your choice of chords is limited by the overall key of the song, yes the melody should probably go with that too. If you use a wider choice of chords, you can match them with a wider choice of notes. And, as well as 'notes from the chord' and 'notes from the scale' a melody will often include chromatic notes, usually adjacent to a more 'allowed' note.

Really, whatever you write, I'll have no trouble finding a theoretical justification for it! The other way around - giving you a set of rules for what notes are allowed, is a lot harder. Theory describes, it does not command.