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The problem it solves
When you see F# in one score and Gb in another and both sound the same, it can look like a mistake. It isn't: it's the same note written two ways depending on the context.
Detailed theory
Key idea
F#=Gb, C#=Db, G#=Ab... one key, two names.
On the piano they sound identical; the name chosen depends on the tonal context.
Understand it
On the keyboard, each black key sits between two white ones and can therefore be named in two ways: the key between F and G is F# (F raised) or Gb (G lowered). Same sound, two names: that's enharmony.
The most common enharmonic pairs are C#=Db, D#=Eb, F#=Gb, G#=Ab and A#=Bb. They all describe the same black key from the neighbouring note on the left (with a sharp) or the right (with a flat).
If they sound the same, why two names? The context. In a sharp key you'll write F#; in a flat key, Gb. Later you'll see that the name also explains where the note is heading, but for now keep the idea: same sound, spelling by context.
It's like a person with two equally valid names depending on who's calling: at home they're called one thing and at work another, but it's the same person. F# and Gb are two names for the same note.
Staff & keyboard
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Another pair: C# and Db. Two spellings on the staff, a single black key.
How to recognise it
How it's written
When two notes with different names land on the same key, they're enharmonic. Look at the key signature and the context: they'll tell you whether to write it with a sharp or a flat.
How it feels
Your ear can't tell F# from Gb: they sound exactly the same. Enharmony is a matter of writing and analysis, not of sound.
Common mistake
Thinking F# and Gb are different notes because they're written differently: on the piano they're the same key.
Choosing the name at random: even though they sound the same, the tonal context decides which spelling is correct.
Try it
On the keyboard, play the black key between F and G and call it first F# and then Gb: the sound doesn't change.
Name each black key two ways: C#/Db, D#/Eb, F#/Gb, G#/Ab, A#/Bb.
On the instrument
Staff & keyboard
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F# and Gb are written in different positions on the staff, but you play the same key. They're enharmonic notes: the sound is identical.
Where it's used
- Understanding key signatures and chord names
- Knowing that the same sound is named one way or another depending on the key avoids confusion.
- Finding the note on the instrument
- Recognising that F# and Gb are the same key when you read different scores.
Examples
Staff & keyboard
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The five black keys, named with sharps: C#, D#, F#, G#, A#.
Staff & keyboard
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And the same five black keys, now with flats: Db, Eb, Gb, Ab, Bb. Compare with the previous example: same keys, other names.
Exercises
Practise enharmonic equivalents
Identify altered notes and locate the black key they correspond to.
Complete 10 attempts · 70% accuracy to pass
Mini test
Check that you've got it.
0/6 answeredQuestion 1/6
What does it mean for two notes to be enharmonic?