When reading a score, notes sometimes carry a small symbol to their left: a ♯, a ♭, or a ♮. These are accidentals — symbols that temporarily alter a note's pitch by a semitone. Unlike a key signature, which applies across an entire piece or section, an accidental modifies only its specific note within a defined scope.
🔑 The three main accidentals
Sharp (♯) raises a note by one semitone. C♯ is one semitone above C. On the piano, it is the black key immediately to the right of C.
Flat (♭) lowers a note by one semitone. D♭ is one semitone below D — the black key immediately to the left. D♭ and C♯ land on the same key; the name used depends on the musical context.
Natural (♮) cancels a previously applied sharp or flat and returns the note to its unaltered pitch. If a note within the same measure was previously sharpened by an accidental or by the key signature, a natural sign instructs the player to restore it to the written pitch without any alteration.
× and 𝄫 — Double accidentals
When a pitch must move two semitones in the same direction, double sharp (×) and double flat (𝄫) come into use. They appear most often in passages that require smooth chromatic voice leading, or in music moving through remote key areas — Chopin and Liszt piano works, and string chamber music, being common sources. Double accidentals are less frequent in standard repertoire but are not rare in chromatic or modulatory passages.
📏 Scope: how long an accidental lasts
An accidental applies only within the measure where it appears, and only to notes on the same line or space as the marked note.
- Within the same measure, all subsequent notes on that line or space carry the accidental automatically. The symbol does not need to be repeated each time.
- At the next bar line, the accidental expires. The key signature's default resumes as if the accidental never occurred.
- To continue the alteration into the next measure, the accidental must be written again.
One exception: if the last note of a measure carries an accidental and is tied to the first note of the next measure, the tie extends the same pitch, and the accidental carries across the bar line for that tied note only.
🎼 Relationship to the key signature
Key signature and accidental operate at different levels of the notation system. The key signature sets the global default: in G major, every F is automatically F♯ unless the score says otherwise. An accidental is a local, temporary override of that default.
If a piece in G major contains F♮ in a measure, the natural sign tells the player to use F — not F♯ — for that note and any subsequent F on the same line or space within that measure. The key signature resumes at the next bar line.
For sight-reading, this layering creates a specific kind of demand. A reader who has not internalized the key signature will miss sharps and flats that the signature implies. A reader who knows the signature well but fails to catch an accidental will produce a different set of errors. Both layers need to be processed simultaneously for accurate reading.
🧠 Why accidentals exist
Accidentals arise because Western tonal music operates within a twelve-pitch chromatic system, while most keys draw on only seven of those pitches as their default set. As music progresses, pitches outside the current key become necessary.
The main situations that generate accidentals:
- Chromatic passing notes — stepwise motion through pitches not in the current key.
- Modulation — when the music shifts to a new key, pitches outside the current key signature appear as accidentals.
- Borrowed chords — drawing briefly from the parallel mode or an adjacent key introduces pitches outside the prevailing set.
Krumhansl (1990) showed that the pitches of a key form a psychological hierarchy in listeners' perception. The tonic is the most stable reference point, and notes grow progressively less stable as they move further from it. An accidental introduces a pitch outside the expected set, registering as tension or a shift in harmonic direction — which is why accidentals carry more meaning than a simple pitch adjustment.
Figure 2: Piano keyboard. Black keys are the sharp and flat notes — each positioned one semitone above or below an adjacent white key. Source: Wikimedia Commons / Public Domain
🎹 Accidentals in sight-reading
Reading accidentals in real time adds a verification step to an already demanding process: does this note have an accidental? Was there one earlier in this measure on the same note? Does the key signature already raise or lower this pitch?
When basic note-position recognition is not yet automatic, this extra layer increases cognitive load and error likelihood. Notes with accidentals consistently take longer to process than unaltered notes in the same passage. The added verification competes for attention with pitch identification, rhythm, and everything else happening simultaneously.
A practical habit: when practicing a passage with multiple accidentals, track which specific altered notes generate errors most frequently. A small set of recurring positions — F♮ in a sharp key, B♮ in a flat key — typically accounts for most mistakes. Focused exposure to those positions reduces error rates more efficiently than replaying the entire phrase.