The difference between the Present Perfect (Simple) - He has seen it - and the Past Simple - He saw it - confuses many students. Problems often arise because some languages have two tenses that seem to correspond to the English tenses, but don't.
When we use the Present Perfect, although the action may be finished (if it's a positive sentence), the time continues up to NOW.
Typical expressions used with the Present Perfect are: today / this year / recently / lately / in the last few days (weeks, etc.) / in the past six months (years, etc.) / yet / already / ever / never / just / so far / up to now / until now / since / for ( = a period up to now)
Have they arrived yet?/ We've had a lot of orders this month. / I haven't seen him lately. / She hasn't phoned since Christmas. / Helen has just gone out. / I've already decided.
She has just gone out. ( = She isn't here.) She went out five minutes ago.
He's done his homework. ( = His homework is finished.) He did his homework before dinner.
I've seen the new James Bond film. ( = I know it.) I saw the new Bond film on Thursday.
All the details - when / where / how much / how / why , etc. - are part of the story, so are used with the Past Simple:
I've bought a car. ( = Now I have a car.) but:
A) When did you buy this car?
B) I bought it last week.
A) Where did you buy it?
B) I bought it in London.
A) How much did you pay for it? etc.
Next Grammar blog: Present Perfect and Past Simple (Part 2)
The Grammar blog is written by Stephen Smith who has been a teacher with OISE for over 10 years. To read more from Stephen, take a look at the following blog posts in the Grammar Series:Verbs not usually used in continuous tenses