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i'm still working with spanish grammar and i happened to encounter these tenses,imperfect progressive and imperfect tense.

when to use and which is which?

let me give you examples of sentences that i encounterd in one of the websites i visited for spanish grammar lesson

Imperfect Progressive:

Lo vi cuando estábamos volviendo.
I saw him when we were returning.

Estaba caminando cuando llamaste.
I was walking when you called.

Él estaba leyendo a las cinco.
He was reading at five o'clock.

Imperfect Past Tense

Hablabas suficiente inglés.- You were speaking enough English.
¿De qué hablabas mientras trabajabas? - What were you talking about while you were working?
Cuando yo vivía en Miami hablaba español todo el tiempo. - When I was living in Miami I used to speak Spanish all the time.
Yo hablaba italiano. - I used to speak Italian.

gracias!

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The imperfect tense is a simple tense:

Verb stem + -aba/-abas/-aba/-ábamos/-abais/-aban (-ar verbs)

Cantaba/cantabas/cantaba/cantábamos/cantabais/cantaban

Verb stem + -ía/-ías/-ía/-íamos/-íais/-ían (-er and –ir verbs)

Escribía/escribías/escribía/escribíamos/escribíais/escribían

The Imperfect progressive is the imperfect of verb “estar” + the gerund of the verb (gerund: verb stem + -ando (-ar verbs) or –iendo (-er and –ir verbs)).

Estaba cantando/escribiendo / estabas cantando/escribiendo / estaba cantando/escribiendo / estábamos cantando/escribiendo / estabais cantando/escribiendo / estaban cantando/escribiendo

Uses of the imperfect tense:

a) descriptions in the past: to talk about the background, the situations and actions that were in development (similar to was/were ...ing in English):

Era tarde. Tenía frío. Veía la televisión pero no podía dejar de pensar en él. Planeaban casarse pero…

(It was late. She was cold. She was watching TV but she couldn’t stop thinking of him. They were planning to get married but…)

b) to talk about general things that used to happen in the past or to talk about customary or repeated actions in the past (similar to used to… in English):

Iba al cine todos los sábados. (He used to go to the cinema every Saturday).

Yo jugaba con ellos. (I used to play with them).

Uses of the Imperfect Progressive:

a) The imperfect progressive describes what the subject was doing or what action or event was taking place for an indefinite period of time.

Estaba jugando con mi hermano. (I was playing with my brother).

Estábamos hablando del accidente. (We were talking about the accident).

b) It is often used to refer to actions which were taking place in the past when something else happened:

Estaba bailando con su novio cuando telefoneó su madre. (She was dancing with her boyfriend when her mother rang).

Anyway, you can usually use the imperfect tense in these cases too, more or less with the same meaning.