Difference between past perfect and past simple with specified time

Question

The rule of thumb that I know about Perfect is that when you use perfect, it doesn't matter when the action was done but what matters is that it was done - the effect. So when I'm saying I've done my homework it doesn't matter WHEN I did my homework just the fact that I actually did it.

However, what happens in that case:

• I've already done it last week
• I already did it last week

In both sentences I mention that I did it last week. Does it mean that the first sentence isn't correct? Or maybe that I should use the second sentence?

Answer 1

The sentence "I've already done it last week." is wrong, since "last" is not used with the present perfect tense and because, as you have mentioned, the present perfect tense is used for an action which happened at an unstated time in the past. So if you want to say "when" you did something, use the simple past tense, as in the second sentence.The only case that we use the present perfect tense for an action which happened within a specific time period is when the action is not over at the moment of speaking.
e.g.I've written two letters this morning. (The time period is not over. It is still morning.)

Answer 2

So when I'm saying I've done my homework it doesn't matter WHEN I did my homework just the fact that I actually did it.

Right, so specifying a time is a bit awkward.

I've already done it last week

Should just be "I've already done it."

I did it last week.

is OK.

Though you will hear "I've already done X {time}" n spoken English a lot, especially as an emphasized form of "I did X {time}." So no one will call you out for being wrong if you say this.

Answer 3

I've already done it last week.

I already did it last week.

Neither sentence is particularly natural in BrE. Already tends to be used with a time period that extends up to a time referred to. The first is very unnatural. A: Do your homework before it gets too late.

B I've already done it.

.

My mother told me (at some time in the past) to do my homework but I'd already done it.