Singing harmony means holding a second line against a melody someone else is singing. It is not the same skill as singing the melody well, and plenty of good singers cannot do it. The reason is simple: when you sing along with a tune, the tune tells you where to go. When you sing harmony, the tune is pulling you toward it the whole time and you have to go somewhere else.

So the skill has three parts. Hearing where your line goes, before you sing it. Finding the first note without being handed it. Staying on your line while the tune moves under or over you. Most advice covers the first part and skips the other two, which is why it does not work.

Start a third above

The easiest harmony to sing is a third above the melody. Your note is two scale steps up from the tune's note, and it moves when the tune moves, so if you can hear the tune you are never far from your note. Play this: the scale, and the same scale a third above it. Solo the top line and sing it, then play both.

What goes wrong

• You drift back to the melody. The tune is louder, more familiar and more interesting than your line, and your ear follows it. This is the big one, and it has its own page.
• You sing the right shape at the wrong height. Your line goes up and down with the tune but starts on the wrong note, so it is a fourth above, or a second. The fix is finding the first note from the chord, not from the tune.
• You are flat on the long notes. Held notes sag. A harmony line has more of them than the melody does, and a sagging third sounds sour in a way a sagging melody does not.

How to practise it

You need three things: a melody that keeps going without you, a way to hear your line on its own until it is in your head, and something that tells you, note by note, whether you sang it. A recording of a friend gives you the first. A piano gives you the second. Almost nothing gives you the third, which is why people practise harmony for years without knowing which notes they miss.

Blend does all three: it plays the tune, lets you hear and read your line, then listens through your microphone and marks every note on the staff as you land it. The first lessons are a third above a stepwise tune, exactly where this page started, and they are free.