A symbol that lowers a note by one semitone, used in key signatures and as an accidental to alter pitch within a measure.
A flat (♭) is a musical symbol that lowers a pitch by one semitone (half step). It appears in two main contexts: in a key signature, where it defines which notes are consistently lowered throughout a piece, and as an accidental placed before a specific note to alter that pitch within a measure. Together with sharps (♯) and naturals (♮), flats are essential tools for chromatic harmony and modulation.
On the staff, the flat symbol resembles a lowercase b and is written immediately to the left of the notehead it affects (or at the start of each staff line in a key signature). A single flat lowers the note once; double flats (♭♭) lower it by two semitones, though these are less common in beginner repertoire.
Musically, applying a flat means moving one key to the left on the piano—or shortening the vibrating length on string instruments, or adjusting fingering on wind instruments—to produce a lower frequency. The interval between a natural note and its flatted version is always a minor second (one semitone).
Key signatures use flats in a fixed order: B♭, E♭, A♭, D♭, G♭, C♭, F♭. This sequence is the reverse of the sharp order and reflects the circle of fifths moving toward flat keys (F major has one flat, B♭ major has two, and so on). Understanding this order helps musicians read signatures quickly and predict which notes will be altered.
The opposite alteration is the sharp (♯), which raises pitch by a semitone. The natural (♮) cancels a previous sharp or flat within the same measure, restoring the note to its diatonic form in the current key.
Flats appear in virtually every genre. In classical music, flat keys such as E♭ major and D♭ major are favored for their warm, mellow color—think of Chopin’s nocturnes or many horn and clarinet parts. Jazz and blues rely heavily on flatted thirds and sevenths (blue notes) to create expressive, soulful lines. Pop and rock use borrowed chords with flatted scale degrees for harmonic color.
Accidentals with flats are common when composers modulate to neighboring keys, introduce chromatic passing tones, or emphasize expressive dissonance before resolution. Reading fluently requires recognizing both the key signature flats and any additional accidentals on the page.
When learning flats, start by naming the affected notes aloud: “B becomes B♭,” “E becomes E♭.” On piano, play the white key and its left neighbor to internalize the semitone drop. For reading, drill key signatures separately from accidentals—know how many flats are in each key before you play the piece.
On string and wind instruments, practice the physical adjustment for each flat until intonation is steady. In ensemble playing, match pitch with others when a passage introduces accidental flats outside the key signature. When you see a natural (♮) after a flat in the same measure, return to the unaltered pitch unless the composer marks otherwise.