What is Melody?
Two songs can use the same chords and same strumming pattern yet still be different. Melody is what will distinguish the two songs and make them different.
What is melody? Notice that if I’d said “Who is Melody?”, I’d have come up with a totally different answer, but that’s not this week’s topic…
When you write a song, there are three different elements. First are the chords. Second is the melody, third the lyrics.
To illustrate this, if you open a songbook, you’ll be faced with something like this:

This is from Pink Floyd’s Money, by the way. Got to try and please the crowd at times. As much as I like Pink Floyd, I can’t stand this song…
At top we have the chords: Bm7 and E/D
The bottom clef is the bass notes as you would play them with your left hand on a keyboard.
There are, obviously, the lyrics and the notes for the voice.
The middle line, though is the melody. It can become a little confusing as in most songs, the melody is simply sung. In this case, the vocals actually sing a different set of notes.
The reason for this is that most songwriters tend to write songs “unplugged”. In other words, they will strum the chords and sing along, never really taking notice of the melody. But, they will write it at some point, even though they don’t really realize it.
In simple terms, when you hear a song and you start humming it, what you are humming is the melody. But what about the instrumental section of the song? Or an instrumental song? (Not really called a song, but rather an instrumental.)
This is where, usually, you’ll find the guitar solo. Most of the time, the solo becomes the melody. Not too confused? Great.
Now a question I often get asked is how can two songs that use the same chords and, basically, the same strumming pattern, be different? This is where the melody comes into play. The melody is what will distinguish the two songs.
As David keeps reminding us, there are many notes in a chord. A melody will use the particular notes of the chord being played.
If, for example, you play an “A” chord, you end up with the notes: A-E-A-C#-E. So your melody will use the notes A, E and C#. Or maybe just a few of them. Say A and E. If I play the A chord, I might write a melody that uses the notes A and C#. Then we’ll jump to another chord, say G: G-B-D-G-B-G. In which case, you might use G-B-G, while I’ll use G-D-B.
So far, using A and G:

Notice the difference?
Of course, as my PC blew up over the weekend and that I’m currently writing this at my girlfriend’s place, I’ve no idea how these sound. What I do know, and you should too, is that just by looking at the notes it should be obvious that these two bits of music will not sound the same.
Then, we could make it a bit different:

And, of course, each time we add a new chord, we add new possibilities. Hence, by using exactly the same chords and the same strumming patterns, twenty people could end up with twenty very different songs.
In copyright infringement suits, the melody therefore becomes primordial. In these cases, judges will look at all three elements: Chords, Lyrics, Melody.
Lyrics aren’t that important. As we’ve seen before, George Harrison once copied a song and changed the lyrics completely.
Chords, well, as we just stated, the same chord progression can make up different songs. Therefore, the melody becomes of prime importance. This is, more often, where a judge will decide whether plagiarism occurred or not.
Now, where do you start: chords or melody?
This will depend on your knowledge of music theory. It’s easier to start with the chords. Your ear will tell you whether or not the melody is right. If you start with a melody, it becomes much more difficult.
If, for example, your melody starts A-C#-E, then you might think that the A chord is your ticket. But, in the make-up of things, it might be that that E belongs to a new chord, leaving you with A-C#. Then you have to know all the chords that contain the notes A and C#. And on, and on throughout your melody.
In the end, you might have a verse that could be A-G-D or Am-G7-Dsus4. Again, I can’t play these at the moment, but I know for a fact that they won’t sound the same.
Which doesn’t mean you should never start with a melody, at times you will have no choice, a certain melody will haunt you until, finally, you write it down. But as you write more and more and hone your particular style, your instincts will guide you and it will be a little bit easier. But, as I said, it will also depend on your knowledge of theory.