Simple Past Tense VS Present Perfect Tense

NEGATIVE​

​ I - You - She - He - It - We - They didn't work yesterday

QUESTION​

​Did I - You - She - He - It - We - They work yesterday

SHORT ANSWER​

​Yes, I - You - She - He - It - We - They worked yesterday

No, I - You - She - He - It - We - They didn't work yesterday

NEGATIVE​

​I - She - He - It was not in class yesterday

They - We - You were not in class yesterday

QUESTION​

​Was I - She - He - It in class yesterday?

Were They - We - You in class yesterday?

SHORT ANSWER​

​Yes, I - She - He - It was Yes, They - We - You were

No, I - She - He - It - wasn't No, They - We - You weren't

[a] Jim has already eaten lunch

[b] Ann hasn't eaten lunch

[c] Have you ever eaten at that restaurant?

In [a] : Jim's lunch occurred before the present time. The exact time is not mentioned, it is unimportant or unknown.

For the speaker, the only important information is that Jim's lunch occurred in the past, sometimes before now

[d] Pete has eaten at that restaurant many times

[e] I have eaten there twice

An activity may be repeated two, several, or more times before now, at unspecified times in the past, as in [d] and [e].

[f] We've been in class since ten o'clock this morning

[g] I have known Ben for ten years. I met him ten years ago. I still know him today. We are friends.

​When the present perfect is used with

In [f] : Class started at ten. We are still in class Now, at the moment of speaking.

Incorrect: We are in class since ten o'clock this morning

SIMPLE PAST

[a] I finished my work two hours ago.

PRESENT PERFECT

[b] I have already finished my work

In [a] : I finished my work at a specific time in the past ( two hours ago).

In (b) : I finished my work at an unspecified time in the past (sometime before now)

THE SIMPLE PAST expresses an activity that occurred at a specific time (or times) in the past, as in (a) and (c)

THE PRESENT PERFECT expresses an activity that occurred at an unspecified time (or times) in the past, as in (b) and (d)

SIMPLE PAST

[c] I was in Europe last year/three years ago/in 2020/in 2019 and 2020/when I was ten years old.

PRESENT PERFECT

[d] I have been in Europe many times/several times/a couple of times/once (no mention of time)

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