Musical simples: This Must Be The Place (Naive Melody)

The song’s subtitle refers in part to its childlike simplicity. Still, there’s more going on here than immediately meets the ear.

If you just look at the top line elements of the song–the guitar part, the vocal melody–then the key of this song appears to be G major. The left diagram below shows G major on the chromatic circle. The right diagram shows it on the circle of fifths. The blue lines show the notes in the bassline, and the brown lines the melody notes.

How do I know that the guitar part implies G major? It goes up and down between the notes G,  A and B–the first, second and third degrees of the G major scale. You can use these notes to play “Mary Had A Little Lamb.” The vocal melody is a little more complex, but it still sounds unambiguously like G major.

The bassline disagrees. The bass notes are D, E, and C, and since the bass usually defines the chord progression, that gives us the chords D, E minor, and C. Since the D is in the metrically strongest position at the beginning of the phrase, you could plausibly hear it as the key center, putting the song in D Mixolydian mode. In that case, the E minor would function as the ii chord, and the C as the bVII chord.

There’s another, equally plausible way to understand the harmony in “This Must Be The Place.” Both of the phrases in the bassline land on the E in their second halves, so you could make a case for E minor as the key center. In that case, D would be the bVII chord, and C would be the bVI.

But what about the melody, you might ask. If we follow that, then the song is in G after all; in this case, D is V chord, E minor is the vi chord, and C is the IV chord. But now we need to accept that the song never hits the tonic chord of its key.

Which key is right? G major, D Mixolydian and E natural minor all share the same seven pitches; deciding which one of them is the central one is ultimately a matter of interpretation. Try playing G major, D Mixolydian and E natural minor over the song, and see whether either one feels the most “correct” to you. I don’t think there is a single correct of the song–the ambiguity is the point. In this case as in all matters of music theory, you ultimately need to let your ear the the judge.