USES OF THE IMPERFETTO
 

REGOLA 1

• The "imperfetto" translates the English expression "I used to": it describes habitual actions in the past, things that used to happen regularly.
   

-- Noi andavamo spesso al parco (We used to go often to the park)
 

-- Loro raccontavano sempre le bugie (They always used to tell lies)

REGOLA 2

The IMPERFECT is used to convey the notion of a "state" rather than an "action". Verbs like AVERE and ESSERE, that normally describe a state "state", are conjugated almost always with the IMPERFETTO.

REGOLA 3

• Combine REGOLA 1 (habitual action in the past) and REGOLA 2 (a description of STATE)
  
  ex. Quando io ero bambino andavo a scuola a piedi
  
  ex. Quando avevo dieci anni andavo in bicicletta tutto il giorno
  
  The verb (essere/avere) describe the state in which you were (you were a kid, you were 10 years old, you were tired etc), the second verb describes a habitual action in past.

REGOLA 4

• IMPERFETTO is normally required for expressions of TIME, AGE, WEATHER in the past (because they describe a state):
  
  Ex. erano le otto di mattina....
  Ex. quando era bambino, Giovanna giocava con le bambole
  Ex. ieri sera pioveva/nevicava/
  Ex. ieri c'era il sole ma faceva freddo
   

All these expressions describe a state.

And now the difficult part

Imperfetto renders the English "past progressive form": ex "I was eating".

If you think about it, "I was eating" describes a STATE not an ACTION.
 

• "I ATE" describes an action that began, took place and ended (completed action).

• "I WAS EATING" illustrates what was taking place, without telling that the action was actually completed. Thus, it describes the STATE of you eating.

• For this reason, because "I was eating" describes a STATE, in Italian it is rendered with the IMPERFETTO: "mangiavo".

The tense that indicates an action that was completed in the past is the passato prossimo.

Ex: "I was eating when the telephone rang"

"I was eating" = state = mangiavo
"the telephone rang" = action = il telefono ha suoanato

While I was in the state of eating, an action began, took place, and was completed.