PRESENT PERFECT OR PAST SIMPLE

(Remember that British and American English have different rules for the use of the present perfect. The comments and the exercises here refer to correct grammar for British English. In American English, it is often considered acceptable to use the past simple in some of these examples.)

The past simple is used to talk about actions in the past that have finished. It talks about 'then' and definitely excludes 'now'.

The present perfect simple to look back on actions in the past from the present. It always includes 'now'.

These sentences are in the past with no connection to the present.

I first got to know him 10 years ago.
I started work here in 1989.
I had too much to eat at lunchtime.
Now look at these same situations seen from the present.

I've known him for 10 years.
I've worked here since 1987.
My stomach hurts. I've eaten too much.
We use time expressions like 'yesterday', 'ago', 'last year', 'in 1999' with the past simple.

We spoke to him yesterday.
He came in a few moments ago.
We made our last purchase from them over a year ago.
She joined the company in 1999.
We use time expressions like are 'ever', 'never', 'since' with the present perfect.

I've never seen so many people here before.
Have you ever been more surprised?
I've done a lot since we last talked about it.
Typical time expressions used with the present perfect in British English but often used with the past simple in American English are 'already', 'just', 'yet'.

I haven't done it yet. (UK)
I didn't do it yet. (US)
I've just done it. (UK)
I just did it. (US)
I've already done it. (UK)
I already did it. (US)
We can use the time phrase 'for' with both forms, but with different meanings.

I lived in Paris for a couple of years before I moved here.
I've lived in Paris for a couple of years and still love it.