I ate tacos yesterday. (Past Simple)
I have eaten tacos before. (Present Perfect)
- We use past simple to talk about events in the past when we know the time.
- We use present perfect to talk about events in the past when we don’t know, or don’t care, about the time.
Notice in the example sentences how the first refers to ‘yesterday’, so we know the time. But in the second sentence, it is just ‘before’ now, so we don’t know the time.
David: Which movie should we watch?
Damien: Let’s watch Spiderman.
David: Yeah, we could, but I have already seen it.
In this conversation the important point is whether or not Damian has seen the film, not when. If he saw it last year, 5 years ago or yesterday it is all the same.
This is quite a useful overview.
This shows how present perfect is used with scenes from TV shows.