Transposition

To transpose is to play or write out a piece in a key other than the one it is written in. You do it to put a piece that is written too high or too low into a key that suits a voice or an instrument. A soprano aria, for example, must be lowered for a contralto, and a song written for a bass must be raised for a tenor.

There are two ways to transpose:

1. by moving the notes to new positions on the staff, when you transpose in writing;
2. by changing the clef, when you transpose while reading, at sight.

1. Transposing in writing

Let's start here, because this is the easier method. First write the key signature of the new key, then copy each note at the required interval, above or below. Along the way you will sometimes need to change a few accidentals, but you have time to think.

Let's go a whole step down first. C major becomes B♭ major, so the key signature has B♭ and E♭. Copy every note a whole step lower. The F# becomes an E that needs a natural, because otherwise the key signature would make it E♭.

Now a whole step up. C major becomes D major, with F# and C# in the key signature, and the F# becomes a G#.

2. Transposing by changing clefs

This is Danhauser's great tool, and the backbone of the French conservatory tradition. It's rarely taught in the English-speaking world, which is a pity, because it is remarkably efficient. The idea is simple. A clef is nothing more than a rule that assigns letter names to the lines and spaces of the staff. If you mentally replace the written clef with a different one, every note on the page instantly takes on a different name, and the whole passage reads in another key. You no longer work out an interval for each note: you just read, in the new clef, what is printed. The method demands fluency in all seven clefs (treble, soprano, mezzo-soprano, alto, tenor, baritone and bass), and it involves three steps:

1. find the clef that lets you read in the desired key;
2. imagine the key signature of the new key in place of the written one;
3. know in advance which accidentals in the music will have to change.

Step one: the clef

Look for the clef that gives the tonic of the written piece the letter name of the tonic of the transposed piece. To transpose a passage written in C into A (a third lower), you need the clef that makes you read “A” where C is written: that is the soprano clef (C clef on the 1st line). In practice, picture the soprano clef in front of the staff: the treble-clef note C in the third space now reads as A, the E on the bottom line reads as C, and so on, all a third lower in name. The clef gives you the letter name of each note but not always its exact octave: you adjust the octave in your head (and on your instrument) to suit the range.

Step two: the imagined key signature

All you need to do is place, in your mind, the key signature of the new key right after the clef. In the example above, going from C major to A major, you imagine 3 sharps in the key signature.

Step three: the accidentals

This is the real difficulty of transposition, so let's take our time. Two precise rules will smooth it out.

The note names that count are those of the notes as you read them in the new clef, not as they are written in the treble clef.

Applying rule 1

Say a passage in B♭ major is to be transposed into G major, a third lower; Danhauser uses an example by Bach. You read in soprano clef, imagining 1 sharp instead of 2 flats. The difference is 2 flats fewer and 1 sharp more, that is, 3 raising accidentals. So any accidental in front of the first three notes of the order of sharps, F, C and G, is raised a half step.

Notice that in the G major version, every accidental in front of F, C or G is played a half step higher than a plain reading in soprano clef would give.

Applying rule 2

Now take a passage in G major, from an example by Cherubini in Danhauser, to be transposed into F major, a second lower. You read in tenor clef, imagining 1 flat instead of 1 sharp. The difference is 1 sharp fewer and 1 flat more, that is, 2 lowering accidentals. So any accidental in front of B and E is lowered a half step.

The two rules confirm each other: the second is simply the converse of the first. Exactly opposite causes produce exactly opposite effects.

Note (k): transposing by a chromatic half step

To transpose up or down by a chromatic half step, you do not change clefs at all: you simply imagine the key signature of the new key. To play in D♭ major a piece written in D major, you replace the 2 sharps with 5 flats; to play in C# minor a piece written in C minor, you replace the 3 flats with 4 sharps.

The two key signatures always differ by 7 accidentals. By rule 1, if the new key has more sharps or fewer flats, all accidentals in the music are played a chromatic half step higher; by rule 2, in the opposite case, all of them are played a half step lower.

Before you try the questions, take a moment to go back over the two rules: they are the heart of this lesson.