What are accidentals?
Accidentals are the little symbols — sharps, flats, and naturals — that nudge a note up or down for a moment. They're how music borrows notes from outside the key, and they're simpler than they look once you know the rules.
Despite the name, accidentals aren't mistakes. They're deliberate, temporary changes to a note's pitch, written right before the note on the staff. Composers use them to add color, tension, and surprise. Reading them accurately is a core skill — and it comes down to just three symbols and a couple of rules.
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1. What an accidental does
An accidental is a symbol placed directly to the left of a note head that changes that note's pitch. The change is temporary — it applies only to that note (and any repeats of the same pitch) within the same measure. There are three you'll meet constantly:
- Sharp (♯) — raises the note by one half step.
- Flat (♭) — lowers the note by one half step.
- Natural (♮) — cancels a sharp or flat, returning the note to its plain pitch.
2. Half steps, the smallest move
To understand accidentals you need the half step — the smallest distance between two notes (think of adjacent keys on a piano, including black keys). A sharp moves a note up by one half step; a flat moves it down by one. So F♯ is the pitch just above F, and B♭ is just below B. On most instruments that's the very next available pitch.
3. How long an accidental lasts
This is the rule beginners most often miss: an accidental lasts for the rest of the measure it appears in — and only at that exact pitch and octave. If you sharp the first F in a bar, every later F in that same bar is also sharp, automatically. The next bar line wipes the slate clean: in the following measure, the note goes back to whatever the key signature says.
4. The natural sign and why you need it
The natural (♮) cancels any sharp or flat — whether from the key signature or from an earlier accidental in the same measure. Say a piece is in G major (every F is F♯). If the composer wants a plain F for one note, they write a natural before it. Sometimes you'll also see a "courtesy" or "cautionary" natural in the next measure just to reassure the player that the alteration is gone. It's a kindness, not a new instruction.
5. Double sharps and double flats
Occasionally you'll meet a double sharp (𝄪, looks like an x) or a double flat (♭♭), which raise or lower a note by two half steps — a whole step. These appear mostly in keys with many sharps or flats, where the spelling of a scale demands them. They're rare for beginners, so don't worry about them yet; just recognize what they mean when they pop up.
6. Accidentals vs. key signatures
It's worth being crystal clear on the difference:
- A key signature applies its sharps or flats to the entire piece, in every measure and octave.
- An accidental is a one-off change written next to a single note, lasting only to the end of its measure.
Think of the key signature as the standing rule and accidentals as temporary exceptions to it.
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7. How to read them confidently
- Scan each measure for accidentals before you play it.
- Remember they last the whole bar at that pitch — then reset at the bar line.
- Treat the natural as "undo whatever was changing this note."
- Practice in short bursts — a few minutes daily beats one long session.
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Frequently asked questions
What is an accidental in music?
An accidental is a symbol — sharp, flat, or natural — placed before a note to raise it, lower it, or cancel a previous alteration, just for that note within the measure.
How long does an accidental last?
It applies to that pitch for the rest of the measure it appears in. The next bar line cancels it, and the note returns to whatever the key signature says.
What's the difference between an accidental and a key signature?
A key signature applies sharps or flats to the whole piece. An accidental is a one-off change written next to a single note, lasting only through its measure.
Keep learning: Read the treble clef · Read the bass clef · all guides · more articles