4 Accidentals and Enharmonics

The seven letters of the musical alphabet name the seven white keys on a piano (as shown in the red rectangles below).

To describe and identify the black notes on the piano, we need to use accidentals. Accidentals are symbols placed directly before a note that modifies the note. The three most common types of accidentals are sharps, flats, and naturals.

When a sharp (#) is placed before a note on the staff, we modify the note by playing it one semitone higher than the original note. A semitone is the smallest available distance between two pitches in music coming from the Western tradition. While there are quarter tones and microtones found in other genres and traditions, Western music theory focuses on the semitone as the smallest available distance.  

When a flat (♭)  is placed before a note on the staff, we modify the note by playing it one semitone lower than the original note.

When writing the note names using letters, the sharp or flat comes after the letter name.

When a natural (♮) is placed before a note, we ignore any accidentals or key signatures (see chapter II) and play the note as it appears on the white keys of a piano.  

Because we can raise or lower a note by a semitone using accidentals, it is possible to have multiple names for the same pitch.