Grace notes — the long and the short

A grace note is a small-print note tucked in front of a full-size one. There are two kinds, and the difference between them is a rhythm question: does the little note steal time from the beat, or does it sneak in just before it?

The two

Name	Symbol	Timing
appoggiatura ("leaning note")	a small note, no slash through the stem, slurred to the main note	lands on the beat, and takes time from the main note — the rule of thumb is half its value (two-thirds if the main note is dotted)
acciaccatura ("crushed note")	a small note with a slash through the stem	crushed in before the beat, as fast as possible, steals no time — the main note still lands squarely on its beat

The appoggiatura is the important one. The weight goes on the small note — it's a dissonance that leans, then resolves onto the main note. Often it matters more than the note it "decorates."

As printed

76 bpm

The small C before the half-note B — no slash, so it's an appoggiatura. (That C is the A string, low 2nd finger.) What you play with it depends on the two readings below.

The appoggiatura, realised

76 bpm

The small C takes the first half of the B's two beats. Play C on the beat — leaning, with a little weight — then let it fall to B. It's a two-note sigh, not a decoration.

The acciaccatura, realised

76 bpm

C is crushed in as fast as possible, right at the end of the D — and B still lands exactly on its beat with its full value. The grace note takes nothing; it just brushes past on the way in.

When the main note is dotted

76 bpm

A dotted B (three beats) with an appoggiatura: C takes two of the three beats, B gets the last one. The 'half' rule becomes 'two-thirds' whenever the main note is dotted.

Try it

Try

Play D (a half note), then C (a quarter) into B (a quarter) — that's the appoggiatura, on the beat, C carrying the weight. Now play D, then a lightning C right before the beat and B full-length on the beat — that's the acciaccatura. Same two pitches, completely different rhythm.

The usual mistake

Playing every small note fast and before the beat. That's the modern, Romantic-inherited habit — and for Mozart the default is on the beat, taking real time. And giving the appoggiatura no weight, so the sigh becomes a hiccup.