Imperfetto or passato prossimo? Italian past tenses
Passato prossimo = something happened (a point). Imperfetto = what was going on, or used to happen (a line).
The imperfetto draws the background, an action in progress with no clear start or end (leggevo, I was reading). The passato prossimo is the event that happens on top of it (è squillato il telefono, the phone rang).
Words that usually go with the imperfetto: da bambino (as a child), di solito (usually), ogni estate (every summer), mentre (while). Words that usually go with the passato prossimo: ieri (yesterday), una volta (once), all'improvviso (suddenly), due volte (twice).
Examples
Da bambino andavo al mare ogni estate.
As a child I used to go to the seaside every summer.
Ieri sono andato al mare.
Yesterday I went to the seaside.
Pioveva e faceva freddo.
It was raining and it was cold.
Mentre cucinavo, è arrivato Marco.
While I was cooking, Marco arrived.
Ho visto quel film due volte.
I've seen that film twice.
Quando eri piccolo, avevi un cane?
Did you have a dog when you were little?
Common mistake
Wrong: Da bambino sono andato al mare ogni estate. Right: Da bambino andavo al mare ogni estate (a habit takes the imperfetto). Wrong: Ho dormito quando hai chiamato. Right: Dormivo quando hai chiamato (I was sleeping — the background).