Which Key Is It In? Tonic Chord

The first step of finding which chords sound good with the given melody is to find out which key is in. It takes some practice, and you'll get a chance to practice right here, on this page.

But first things first.

Tonic: a “home base”

There are no strict rules in music, and there are melodies that are not that easy to figure out–I won't even start talking about jazz, for example–but the majority of the popular music follows some basic concepts.

One thing you need to start feeling is when a melody is in an “unstable” place and wants to “resolve” to some other note, and when it feels “complete” and “at home”. Let me give you a simple example. The following score gives you the first two phrases of “Happy Birthday”. I marked an “unstable” pause with red, and a ”stable”, “home” note with blue. Can you hear that?

You don't need to know how to actually read the sheet music for this tutorial, just follow the melody!

The first half ends at B and it does not feel complete there, and when the second half ends at C, the melody feels more stable. If we look at the next phrase, we'll see it goes back to C at the end again:

We can conclude that C sounds like a special, stable, and “home base” note for this melody. Also, the melody is generally “happy”, not “sad” at all, so it's major, not minor. If we try to play the C major chord when the melody goes to its “home base”, it should sound right.

Play the C chord only when the melody approaches the blue notes, marked as C:

A “home base” note is called a tonic, and the major or minor chord–the one that fits the melody best–is called a tonic chord. For this version of “Happy Birthday”, we say that it's written in C major key, and its tonic chord is C major chord.

You can play any melody in any key, it's called transposing. Here's the same “Happy Birthday”, but in a different key. Can you guess what is the tonic here?

The answer is (click to reveal) D major: it's one whole step higher from the C major version.

Practice

Let's try some other songs. First, “Go Down Moses”: find a tonic; is it major or minor?

The “home base” of this melody is its last note, A, and it's in minor, so the answer is A minor.

Let's do one more. It's the second phrase of “Greensleeves”, and I transposed it into some random key. Which one?

Here, the answer is D minor, because this is where the melody comes “home” when it reaches its last note.