What is the difference in meaning between:
1-"He didn't play tennis last week."
2-"He didn't play tennis a week ago."
Adverbials with ago establish a closer relationship with the present, as if we could draw a timeline between that moment and now. In fact, ago means "at a certain time before now."
Instead, adverbials with last refer to that point in the past, and are preferred when reference to the passage of time is not necessary.
. . . a very obvious difference could be the quantity of time.
If today is Monday, last week could refer to something that happened on Friday, for example. That is 3 days ago.
One week ago for me = 7 days ago and is, therefore, more specific.
Actually, "last week" could refer to any day last week — it could be the case that he plays every day, and that he didn't play a single day during the period defined as "last week."
I understand your point about "a week ago" being more precise and therefore less frequent than "last week," but the fact that it carries the connotation discussed further above is undeniable — most speakers will say "I didn't play tennis last week" rather than "I didn't play tennis a week ago" even if they mean to say "I didn't play tennis this day last week."
Hi, all—EG, you have raised an important point. From the point of view you are looking at the sentences, "I didn't play tennis last week" does have a much more general application, and that is worth pointing out. Indeed, its more general applicability explains the grammaticality difference between these sentences:
(3a) I didn't play tennis at any point in time last week.
(3b) *I didn't play tennis at any point in time a week ago.
That said, the assumption I was making was that the OP, Ahmed.A.A, wanted to know what difference in meaning the two sentences have in a situation where the one sentence might be used instead of the other, and that would be a situation in which it was understood that "last week" picks out a particular day.
Let me explain that a little more, in case it is unclear to anyone. As we all know, people tend to have things that they do on certain days of the week. For example, somebody might have band practice every Tuesday night. For such a person, "I didn't go to band practice last week" would mean "last Tuesday."
Similarly, it seemed to me that the speaker of Ahmed.A.A's had a regular tennis-playing day of the week in mind, one that was precisely a week prior to the time of speech. In that kind of context, it is possible to use either "last week" or "a week ago"; however, the important contrasts Gustavo has observed exist.