A verb construction (made up of a past form of the verb "to be"--"was" or "were"--plus a present participle) that conveys a sense of ongoing action in the past. The simple past tense (for example, worked) is used to describe an action that has been completed. The past progressive (was or were working) is used to describe an action that was in progress at some point in the past. See also:
Examples and Observations:
- "I was working on the proof of one of my poems all the morning, and took out a comma. In the afternoon I put it back again."
(Oscar Wilde) - "I was reading the dictionary. I thought it was a poem about everything."
(Steven Wright) - "I decided to become an actor because I was failing in school and I needed the credits."
(Dustin Hoffman) - At the very moment that the iceberg struck, the saloon passengers were singing 'A Life on the Ocean Wave.'
- "Often the action expressed with the past progressive was ongoing at the time another action occurred. In such cases, the action that occurred is expressed with the simple past, and the sentence generally includes a subordinate clause that begins with when or while. With when, the past progressive action can be in the main clause, as in (39a), or in the subordinate clause, as in (39b).
(39) a. He was studying for his exam when I saw him this afternoon.
Although most textbooks stress the use of the past progressive in sentences like those in (39), quite frequently the past progressive is used in sentences like (40), in which two ongoing actions in the past were occurring simultaneously:
(39) b. She accidentally cut her hand while/when she was chopping vegetables for a salad.(40) She was studying in the library when I was talking to Tom."
(Ron Cowan, The Teacher's Grammar of English, Cambridge University Press, 2008)

