To play harmony on a piano, you have to play two or more notes, some interval apart, at the same time. Try playing the notes of each interval — perfect, diminished, augmented, major, and minor — as shown in the following figure at the same time.
They sound perfectly lovely, but how do you use these intervals to create harmony? You can
Add intervals to the right hand under a melody line.
Play intervals in the left hand while the right hand continues the melody.
Do both.
Notice that the notes in each interval are stacked. When two notes appear stacked, or attached to the same stem, you play them at the same time. You know, in harmony.
You don’t have to figure out how or when to add intervals to a melody. The composer does that for you and notates these intervals in the printed music you play. But you should understand that all these intervals combine with the melody to make a very harmonic tune. Sure, you could just play the melody by playing only the top note of each group of notes, but your audience will appreciate the extra effort of playing the intervals. Besides, why do you think you have so many fingers?
Of course, if you want to add intervals to a melody yourself, try choosing the interval either a third below or a sixth below the melody note. And, one of the easiest ways to do that is to play single notes with the left hand that form intervals when combined with the right-hand melody notes. Often, you simply play one note with the left hand and hold it for several measures as you continue with the melody. However, you can fill out the sound even more by adding a harmonic interval to the left-hand part.
To give a song a little more movement, you can play a harmony part in the left hand that matches the melody note-for-note. Or go for four-part style with simple intervals in both hands. Just a couple of notes create a nice, full sound:
