Sharps, Flats and Naturals: Accidentals Explained Simply

A sharp (♯) raises a note by a half step, a flat (♭) lowers it by a half step, and a natural (♮) cancels any sharp or flat and returns the note to its plain letter name. When one of these signs appears next to a note in the music, it's called an accidental, and it lasts until the end of that bar.

Those two sentences cover most of what you need. The rest of this guide explains the details that trip beginners up: what counts as "the same note", how accidentals differ from the key signature, why one key can have two names, and how all of it shows up in the first bar of Für Elise. If you're still learning the note names on the staff, read the beginner's guide to reading sheet music first.

The three signs at a glance

A half step is the smallest distance on a piano: from one key to the very next key, black or white.

The sign always sits on the same line or space as the note it changes, just to the left of it. In writing, we say "F sharp" and write F♯, but on the staff the sharp comes before the note.

Most of the time a sharp or flat lands on a black key. Two pairs of white keys have no black key between them (E and F, B and C), so E♯ is the same key as F, and C♭ is the same key as B. You won't see those often as a beginner, but now they won't surprise you.

How long an accidental lasts

Here's the rule most beginners miss: an accidental doesn't just affect one note. It applies to every later note on the same line or space, in the same octave, until the bar line.

Picture a bar with four Fs on the top line of the treble staff:

1. First F has a sharp → F♯.
2. Second F has no sign → still F♯, because the sharp lasts to the bar line.
3. Third F has a natural → F.
4. Fourth F has no sign → still F, because the natural now lasts to the bar line.

At the bar line everything resets. The exception is a tie: if the last note of a bar is tied to the same note in the next bar, the accidental carries into that tied note only.

Composers and editors often add a "courtesy" accidental in the next bar, sometimes in brackets, to remind you that the note is back to normal. It doesn't change anything; it just saves you from a wrong note.

Key signatures vs accidentals

Sharps and flats show up in two places, and they behave differently.

• Key signature: the group of sharps or flats right after the clef at the start of every line. It applies to every note with that letter name, in every octave, for the whole piece (until the key signature changes).
• Accidental: a sign written next to one note in the music. It applies only for the rest of that bar, in that octave.

So if the key signature has one sharp on the F line, every F in the piece is F♯ unless an accidental says otherwise. Before you play anything, look at the key signature and say out loud which notes it changes, for example "all Fs are sharp". It's the most common source of wrong notes in sight-reading.

Enharmonic notes: one key, two names

Every black key has two names. The black key between C and D is both C♯ and D♭. Notes that sound the same but are written differently are called enharmonic equivalents.

Why two names? Because the written name depends on context. In a key that uses sharps, composers tend to write sharps. A melody climbing up often uses sharps, and one moving down often uses flats. On a piano you press the same key either way.

Worked example: the opening of Für Elise

Beethoven's Für Elise (Bagatelle No. 25 in A minor, WoO 59, dated 1810 on the Wikipedia page) opens with one of the most famous accidentals in music. The right hand starts with a fast back-and-forth:

E – D♯ | E – D♯ – E – B – D – C | A

The first two notes are a pickup before the first full bar. Read it with the rules above:

1. A minor has no sharps or flats in its key signature, so every note is natural unless marked.
2. In the pickup, the D has a sharp sign → D♯, a half step below E.
3. The bar line resets everything, so the score writes the sharp again on the D♯ in bar 1. Without that sign, it would be a plain D.
4. Later in bar 1, D appears again. The sharp from earlier in the bar would still apply, so the score adds a natural sign: D♮.

That natural sign in bar 1 is the rule in action. Beginners who skip it play D♯ a second time and the phrase sounds wrong. Wiggling between E and D♯ is a half step, the smallest possible move on the piano, which is why the opening sounds like a nervous shimmer.

To practice the shimmer, import a Für Elise MIDI and play it in Note Bounce, naming each note as the ball lands on it, including "D sharp" out loud. The Für Elise reading guide covers the rest of the A section.

If you want to see that E–D♯ wiggle as motion rather than notation, try it in Marble Music (formerly Beat Bounce), which turns MIDI files into bouncing-marble videos where the marble hits every note. Its free MIDI library includes Für Elise files you can use there or import into Note Bounce. Browse the Marble Music MIDI library.

Quick self-check

Cover the answers and try these. In the key of C (no sharps or flats):

1. A bar has G♯, then G with no sign. What's the second note? (G♯)
2. A bar has B♭, then B with a natural sign, then B with no sign. What's the last note? (B natural)
3. Next bar, B with no sign. What is it? (B natural, because the bar line reset everything)
4. What's another name for E♭? (D♯)

Three out of four means you've got it. Now open any piece and circle the accidentals before you start reading. When you're ready for whole groups of sharps and flats, the key signatures guide shows how to name the key in seconds.