The Perfect is used with situations before a certain moment:
But the Present Perfect shares the same 'territory' with the Past Simple and there are special rules for these tenses:
We use the Past Simple with words for a finished time. We use the Present Perfect with words for time up to now:
With time expressions like today or this month we normally use the Present Perfect, but these expressions can refer to a finished time:
Without a time expression, the two tenses show that the period of time connected to our situation is finished or unfinished:
We use the Present Perfect for permanent/serial situations that continue until now:
We often use the Present Perfect for singulary situations which are recent:
Especially if they have a present result:
The Present Perfect is replaced by the Past Simple when we continue talking about the same situation:- Have you seen the Egyptian Exhibition?
We use the Past Simple to ask When...? or What time...?:When did J. K. Rowling publish her latest book?