I thank you but unfortunately I cannot.
pur-TROP-po — stress on second syllable. 'Purtroppo' = unfortunately.
Decline an invitation or request politely in formal Italian contexts. The combination of thanks + 'purtroppo' is the most gracious way to say no in Italian without giving offence.
Italian refusals follow a specific etiquette: always thank first, always add 'purtroppo' (unfortunately) to signal regret, and optionally give a brief reason. A bare 'no' without these elements sounds abrupt and possibly rude. The reason given need not be detailed — 'ho un impegno' (I have a commitment) is sufficient.
Purtroppo ho già un impegno.
Unfortunately I already have a commitment.
'Ho un impegno' is the perfect Italian excuse — vague but accepted.
Mi dispiace, non potrò esserci.
I'm sorry, I won't be able to be there.
For declining invitations to events.
Sarà per la prossima volta.
It'll be for next time.
Closes the refusal positively — implies future willingness.
Italian social refusals are an art form. The phrase 'ho un impegno' (I have a commitment) never needs elaboration — asking what the commitment is would be intrusive. The exchange of refusal and counter-invitation ('sarà per la prossima volta') is a socially complete ritual that leaves the relationship intact.