Past Simple or Present Perfect

Why the rule does not help

The usual explanation is that present perfect is for actions connected to the present. True, and almost useless in the moment — every action you care about feels connected to the present, or you would not be mentioning it.

A better question is available, and it is about time rather than about the action.

The question: is the time period finished?

Not the action — the time. If the stretch of time you are talking about is closed and gone, use past simple. If it is still open, use present perfect.

I wrote three emails yesterday. Yesterday is over; the box is sealed. Past simple.

I have written three emails today. Today is still running; more emails may yet arrive in it. Present perfect.

Notice that the action is equally finished in both sentences. What changed is the container it sits in.

Why "I have seen it yesterday" is wrong

This is the single most common mistake, and the question above explains it in one move. The word yesterday names a closed period, so the sentence has to be past simple: I saw it yesterday.

The same goes for last year, in 2010, two days ago, when I was a child — all sealed boxes, all past simple.

It also explains a rule people memorise separately: a question starting When…? takes past simple. Asking when something happened means you are asking which finished moment it belongs to, and that moment is by definition closed.

Meanwhile just, already, yet, ever, never, so far and recently all avoid naming a time at all, which is why they sit so comfortably with present perfect.

for and since, and the trap inside them

since marks a starting point: since 2010, since Monday, since I moved here. for marks a length: for ten years, for twenty minutes.

Now the part that actually changes meaning. I lived in Berlin for ten years says you no longer live there — closed box. I have lived in Berlin for ten years says you still do.

Native speakers hear this difference without thinking about it, so getting the tense wrong here does not sound like a grammar slip. It sounds like a different fact.

been to and gone to

She has been to Japan — she went and she is back. The trip is an experience she now owns.

She has gone to Japan — she went and she is still there. Do not expect her in the office.

One letter of difference in the sentence, a whole different answer to "where is she?"

The one mechanical thing to get right

After have or has comes the third form of the verb, the past participle — not the past simple form. I have gone, not I have went. She has seen, not she has saw.

For regular verbs the two forms are identical and nothing can go wrong. For irregular verbs they differ, and this is where most written mistakes actually happen — not in choosing the tense, but in building it.