The passato prossimo and the imperfetto are often used together in accounts of past events. They express different kinds of actions in the past, and cannot be used interchangeably
1. The passato prossimo is used to describe specific events in the past. It tells what happened at a given moment.
Ieri ho ricevuto tre lettere Yesterday I received two letters
Siamo usciti alle otto We went out at eight
2. The imperfetto describes habitual actions in the past. It tells what used to happen.
Scrivevo una recensione per un giornale ogni sabato.
I used to write a review for a newspaper every saturday
It also describes ongoing actions in the past; what was going on while something else was going on or what was going on when something happened.
Io guardavo un DVD mentre mio cugino ascoltava la radio
I was watching a DVD while my cousin was listening to music
Mangiavate quando ho telefonato?
Were you eating when I called?
The imperfetto also relates conditions or states physical or mental-in the past, such as appearance, age, feelings, attitudes, beliefs, time, and weather.
3. Because the passato prossimo expresses what happened at a particular moment whereas the imperfetto expresses a state of being, the passato prossimo is used to indicate a sudden change in a state of being
Avevo paura dei topi I was afraid of mice (mental state)
Ho avuto paura quando ho vistoil topo I got scared when I saw the mouse
4. Notice that for the verbs dovere, potere, and volere, the use of the passato prossimo indicates what did or did not happen while the imperfetto indicates only a mental state or intention.
Dovevo fare i competi deciso fare i competi
I was supposed to do my homework but I decided to go out
Marco Voleva studiare in italia ma non aveva i soldi
Marco wanted to study in italy but he didn’t have the money
5. Looking for the following patterns will help to decide whether to use imp or pp
Imp + mentere + imperfetto = 2 actions happening at the same time
Imp + quando+ pp = interupted by another action