Enharmonics · Accidentals · Music theory
Two notes are enharmonic when they sound the same and are written differently: D♯ and E♭, E♯ and F, B♯ and C. On the piano they are the same key, but not…
Enharmonics
Two notes are enharmonic when they sound the same and are written differently: D♯ and E♭, E♯ and F, B♯ and C. On the piano they are the same key, but not the same note.
The music decides the name, not the sound: the interval it forms, the key and where the note goes. C–D♯ is an augmented second and C–E♭ a minor third; that is why this site always writes and checks the written note, and B♯3 keeps its octave even though it sounds like C4.
Why they can sound the same
Enharmonics are a child of temperament. If twelve pure fifths are tuned in a row, you do not return exactly to the starting note: a little is left over, about 23 cents, called the Pythagorean comma. In those tunings, D♯ and E♭ were two slightly different notes.
Sharing that difference among all the notes makes the two coincide. Singers and string players can still shade them, and often tune a leading tone a little higher than the enharmonic note that tends to fall.