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Accidentals modify a note's pitch by a half step: a sharp (♯) raises a note by one half step, a flat (♭) lowers it by one half step, and a natural (♮) cancels a previous sharp or flat. Enharmonic equivalents are notes that sound identical but are spelled differently (e.g., F♯ and G♭). Choosing the correct spelling depends on the musical context, particularly the key signature and harmonic function.
On a piano keyboard, identify all the black keys and practice naming them both as sharps and flats. Write out enharmonic pairs and play them to confirm they sound the same.
You already know that notes have names — A, B, C, D, E, F, G — corresponding to the seven white keys of the piano, which repeat across octaves. Accidentals extend this system to the black keys. The piano keyboard has a systematic pattern: between most pairs of adjacent white keys there is a black key, but there is no black key between B and C, or between E and F. Those pairs are already a half step apart — the smallest interval in standard Western tuning. Where a black key exists between two white keys, those white keys are a whole step apart, and the black key can be named in two ways: either as the sharp of the lower note or the flat of the upper note.
A sharp (♯) raises a pitch by one half step. A flat (♭) lowers it by one half step. A natural (♮) cancels any preceding sharp or flat, restoring the note to its unaltered white-key pitch. Within a measure, an accidental applies to every subsequent occurrence of that note at the same octave until the bar line — so if F is sharped on beat one, every F in that measure is also F♯ unless a natural sign appears. This scope rule is the most practically important thing to internalize for reading music.
Enharmonic equivalents are the key conceptual insight: two different spellings can refer to the same physical pitch. F♯ and G♭ are played on the same piano key and produce the same frequency in equal temperament. Similarly, C♯ = D♭, D♯ = E♭, G♯ = A♭, and A♯ = B♭. Even white-key notes have enharmonic spellings: B♯ is enharmonically C, and C♭ is enharmonically B. Why would musicians use one spelling over another if they sound the same? Because spelling communicates harmonic context. In the key of G♭ major, you write A♭ — not G♯ — because the key contains flats, and writing G♯ in a flat context creates unnecessary confusion for the performer. The spelling tells you where you are in the tonal landscape before you've played a note. If you've studied modular arithmetic, you can think of the 12 pitch classes as positions on a clock face, where enharmonic equivalents are different names for the same position — the name you use depends on which direction you arrived from.
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