Have you met someone with the magical ability to play along with any song or tune they like?

These people have probably not done a deal with the devil, but have instead learned about the primary triads.

As long as you know the three primary triads belonging to a particular scale or key, you can successfully harmonize any melody based on that scale/key.

For both major and minor scales/keys the primary triads are those build on the first, fourth and fifth scale degrees of that scale.

Any Questions?