Past perfect tense and simple past tense

[alfree]

Hi,

May I know the difference between the use of past perfect and simple past?

a. Mary had completed her work.
b. Mary completed her work.

Does statement (a) indicate that the work was completed some time ago, while statement (b) indicate that the work was completed in the past (time could be some time ago, or recently)?

[5jj]

a. Mary had completed her work.
b. Mary completed her work.

a suggests that the work was completed before another past time known to us. The sentence is unlikely to be uttered without more context.

b tells us simply that the action was completed before the present time. Once again, the sentence is unlikely to be uttered in isolation. Context would make the time of the completion clear.