When can contractions be used in Italian?

Well, in italian when two vocales (one in the end of the word and one beginning) sometimes there's a elision. (The contraction is an another thing).

Cos'hai fatto? (Cosa hai fatto?) means What did you do? (singular)

Cos'hanno fatto? (Cosa hanno fatto) means What did they do?

In italian H inizial word is changes

I do some examples...

C'è <----- Is "ci è".......look i final word and e initial word....so we say "c'è" not "ci è" because it's shorter....it's like There's and There is....but both are correct

Cos'hanno fatto? <---- Is "cosa hanno fatto?" ....look a final word and h initial word (remember, it's changes!)....so we say "cos'hanno fatto?" because is shorter, but we say "cosa hanno fatto?", too, and it's correct, too...

If you understand italian you can tead this http://www.treccani.it/enciclopedia/elisione_%28En...

Sorry for my english!

Bye!

I don't see why "Cos'hanno fatto?" should be any less legitimate than "cos'hai fatto".

Contraction rules are so simple and the number of possibly affected words is so high that no list can ever be compiled.

Basically: between articles (la, lo, gli, uno, una) and nouns the encounter of vowels is to be avoided. l'amicizia, l'eroe, un'amica.

then there are other shorts words like ci (che c'é?) whose vowel gets the kick,

or frequent phrases like cosa: "che cos'é?" - but in tzhese cases, the elision is optional: che cosa hai fatto, che cosa hanno fatto will in spoken Italian always sound like /che cos'ai fatto/ - /che cos'anno fatto/ no matter how one writes it.

Italian Contractions