Lessons › Theory

Sharps, flats and naturals explained

An accidental is a sharp, flat or natural written in front of a note. It changes that note by a half step, and it keeps working until the end of the measure.

The three common accidentals

• Sharp (♯) raises a note by a half step. On a piano, that is the very next key to the right, black or white.
• Flat (♭) lowers a note by a half step, to the next key on the left.
• Natural (♮) cancels a sharp or flat, so the note goes back to its plain letter.

The accidental is written before the note on the staff, on the same line or space as the note head, but we say it after the letter: F sharp, B flat. That small mismatch trips up beginners, so make a habit of looking just to the left of every note.

How long an accidental lasts

An accidental applies to every later note on the same line or space for the rest of the measure. At the next bar line it stops, and the note goes back to whatever the key signature says.

Two details catch people out:

• An accidental only applies to the same written position. A sharp on F4 does not affect F5 an octave higher, at least in modern notation.
• A note that is tied across a bar line keeps its accidental for the tied note, even though it is in the next measure.

Courtesy accidentals

Because the rule is easy to forget, editors often add a courtesy (or cautionary) accidental in the following measure as a reminder: a natural, sometimes in brackets, on a note that would be natural anyway. It changes nothing; it just saves you a second look.

Accidentals and key signatures

A key signature is a set of sharps or flats that apply to the whole piece, in every octave. An accidental overrides it for one measure. So in G major, where every F is sharp, a natural sign in front of an F makes that F (and later Fs in the same measure) plain F. The key signatures lesson explains how to read them.

Double sharps and double flats

A double sharp (written like a small bold x) raises a note by two half steps, and a double flat (♭♭) lowers it by two. They appear in keys that already have many sharps or flats, where a note needs to go one step further. F double sharp sounds the same as G on a piano, but it is written as an F because of its place in the scale or chord.

Enharmonic notes

Two names for the same pitch are called enharmonic: C♯ and D♭, E♯ and F, B and C♭. They sound the same on a piano, but they are spelled differently depending on the key. A melody in A major uses C♯; one in A♭ major uses D♭. Reading becomes easier when you expect the spelling the key uses.

Reading accidentals at sight

• Scan the measure before you play it. Accidentals stand out; notice them before you arrive.
• Remember the bar line resets them. If a passage keeps one note sharp across several measures, each measure gets its own sign.
• Think in shapes. A melody that goes up a half step with a sharp is often leading somewhere, usually up to the next note.