Last Monday

Last Monday
 

Last Monday I went to the cinema
I ve been going out a lot for the last few weeks.


If a student asks you why do we use the article in front of last in the second sentence and not in the first one, what would be the answer.?

In English if you put the in front of last Monday, it requires further clarification often with a prepositional phrase, and the meaning changes. For example: the last Monday of the month (el ultimo lunes del mes) instead of just last Monday which is el lunes pasado. If followed by a verb, the meaning changes similarly. For instance: the last Monday I saw you means el último lunes que te ví.

Good question. I think it just boils down to collocation.

The second time 'last' is used, it is paired with 'few'. That collocation requires the use of an article.

By the way, the preposition 'for' isn't needed.