Time to show my ignorance.

My son is doing Grade 4 and has just started on Georg Benda's Allegro assai: 3rd movt from Sonata in G. I've been helping him by showing him some of the more difficult bits, but he came back from his latest lesson telling me that I was wrong. Turns out that what I'd interpreted as grace notes (acciaccaturas) were, actually, appoggiaturas. I've always completely failed to understand the appoggiatura - I mean, if you mean it to sound like two semi-quavers why not write two semi-quavers?

Anyway, if anyone has any hints, tips or tricks on a) how to recognise them, and b) how they are supposed to be played, I'd be very grateful. And that's me, with merit in Grade V theory and Grade 8 piano!

Shucks.

Edward

I think they appear in situations where the composer wants to use a note that's not 'allowed' harmonically, so has to put them in as an ornament (which is allowed).

Recognising them needs keen eyesight:
Appoggiaturas are little notes.
Acciaccaturas are little notes but with a diagnoal line through them.

You can see pictures here

Acciacaturas have crosses through them, whereas appogiaturas don't, although sometimes one is written when the other is meant

I think, in general, you play them as half the length of the note after it, or two thirds if it's other note is dotted. But there are exceptions to the rule as usual.

I think one of the points of appoggiaturas is that you can, in theory, omit them without effecting the structure of the melody.

Appoggiaturas should generally be half the value of the note before it (or a third if the note is dotted as mentioned above) whereas acciaccaturas would usually be played quickly, almost 'crushed' into the next note.

But it varies depending on what would be suitable for the piece.

One of the variations is treatment before dotted notes: C P E Bach suggests the appoggiatura takes 2/3 of the time value. This often sounds better to me, but others may disagree.