Chords to a song

[Hannu]

If you have a song which has only the melody (the singing) how do you know what chords you have to play? I know you can listen what sounds good (and thats how I've done it) but I wonder what kind of logical RULE there is for that.? It's all about harmony right? Cause you dont change the chord everytime when a different note comes.

Is there something else to do than listen?

[The Fury]

I suppose you'd have to know the notes the voice was singing. You could either work them out (same way you would work out a solo) or use some sheet music. Then by knowing what key you're in, try and experiment with chords of that key.

Perhaps start off with simple harmonies like thirds or fiths and if that didn't sound right move on to more abstract ones.

I don't know about this, I've never tried it.

[Hannu]

Thanks, but I knew that already :D
The question was about the exact rule "the mathematic". Can you count the right chord somehow from the melody... eh... :p
Sorry, I didn't write it too clearly. But thanks for your replay