How to Tell the Key of a Song

Question: Hello Albert,

Many years ago, I was taught that by looking at the last note or notes of a piece of music, one could tell what key it is in, that is of course if one does not understand the key signature in the beginning of the piece of music.

That being said, I am practicing a piece of music from Chopin that it is written in F minor. I know its relative major is A, right? It also ends in A.

I am finding it difficult to describe this, but why is music written like this, please?

Why not just write the music in A and call it (Title) in A?

Many thanks,

– Brian (Colombia, South America)

Albert’s reply: First and foremost, musical forms are by nature dramatic, not prescriptive! There’s no rule that states that a piece of music must end in the same key in which it starts. (It just happens to be a convention, such as for Classical – meaning the Classical era, a small subset of what we call “classical” music – sonata form.)

Chopin broke with convention in his Second Ballade. It starts in F major yet ends in A minor. Generally it’s cataloged as Ballade No. 2 in F major, Op. 38, but Murray Perahia listed it as Ballade No. 2 in A minor, Op. 38 in his recording of Chopin’s Ballades.

You can calculate the relative minor of a major key simply by taking the note a minor third lower than the tonic. The relative minor of C major is thus A minor, since A is a minor third lower than C.

The reverse also holds, of course. The relative major of a minor key is a minor third higher than the tonic. C major is thus the relative major of A minor, since C is a minor third higher than A.

The relative major of F minor is thus A-flat major, since A-flat is a minor third higher than F.

Make sure you study the key signature chart and the Circle of Fifths so that you’re very familiar with all of the keys.

Also, looking at the final chord of a piece in order to tell what key it’s in is only a rough guideline. Many pieces in the minor mode end in the parallel major. An example is Baroque works that end with the so-called Picardy third, in which the third scale degree in a work in the minor mode is raised, making the final chord major. For example, a piece in F minor might end in the parallel major, F major.

Nor is looking at the first chord entirely reliable. Beethoven starts his Piano Sonata in E-flat major, Op. 31, No. 3, with an inverted minor seventh on the second scale degree (minor ii 6–5)! Less radically, some works, even Classical-period movements in sonata form, avoid reaching the “real” key of the movement until after an introduction is played. Beethoven uses this strategy in the previous sonata in that opus, the “Tempest” Sonata, Op. 31, No. 2. The “Tempest” Sonata starts on the dominant (in this case an A major chord), with material that is designed to imitate operatic recitative. The effect is of an improvised introduction before the home key of D minor is reached, at which point the “real” sonata commences.

Finally, a key signature does not always correspond to the Circle of Fifths, which depicts major and minor keys only. The first movement of Bach’s Violin Sonata in G minor is not in G minor, despite its key signature of two flats! Instead, Bach uses D Dorian, which also has two flats. To simplify, you could take any key signature, write out the pitches A through G, and start the scale on any note. Each scale thus produced would be one of the music modes.

Ultimately, the only true solution to determining the key of any piece of music is to learn harmony, key signatures and musical forms. Always remember that harmony is not about technical rules on paper but primarily about what we hear and how we hear.

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