Where do great melodies come from? This may be one of the biggest riddles of songwriting. We all use the same twelve notes, but the order and duration of those notes makes for an infinite number of possible melodies. Great melodic ideas can result from a number of different writing approaches.

Inspiration

Sometimes you get lucky; divine providence gives you a hint, the subconscious takes over, or the muse speaks through you. However you choose to look at it, there are times when it just happens. While you can't make it happen, you can learn how to let it happen. Whenever you get an inspired melody, write for as long as the feeling lasts, then look for any factors that might have put you in the right frame of mind. Was it a hot bath? Knowing you have the day off tomorrow? Learning a new chord? Were you just whistling and — poof! — a brilliant melody appeared? Find out what gets your muse working and set aside time for those activities.

Invention

If you put a hundred monkeys plunking away at a hundred pianos for an unlimited amount of time, eventually one of them would come up with a perfect melody. Of course, the monkey's publisher would want a rewrite and the other monkeys would immediately come up with curiously similar melodies, but that's not the point. Whether you sing, whistle, or play an instrument, just goofing around and making mistakes will often yield surprising results. When you find something, try variations of the original idea or play around some more in the same mode. Hopefully, at some point, inspiration will take over.

Innovation

You can't use someone else's melody for your song, but you can use it as a starting point for experimentation. Existing songs can be a rich source of melodic ideas. Listen to your favorite songs or to the radio, notice how different songs approach and develop melodic ideas and how they use various modes, meter configurations, and other elements. One great exercise, used by Paul Simon, is to play a harmony to an existing melody, then change and develop it until it becomes a totally different song.