Dewi & Dono : Present perfect VS past simple

Dewi :

Dono, I'm a bit confused about my sentences below:

1. I wrote a letter.

2. I have written a letter.

What is difference between these two sentences?

I know that 1) is in simple past tense and 2) is persent perfect.

But, both as I think suggest that work has completed in past. What is the difference between present perfect and past simple, Dono?

Dono

Well, there is more than one difference between the simple past and the present perfect. The simplest difference is the grammatical difference that the simple past can be used with expressions which signify a definite, particular time in the past.

I wrote a letter yesterday.
I wrote a letter at 7 o'clock.
I wrote a letter last Monday.
I wrote a letter several weeks ago.

The present perfect cannot be used with such expressions. (After all, it IS a "present" tense!)

I have written a letter yesterday. (X)
I have written a letter at 7 o'clock. (X)
I have written a letter last Monday. (X)
I have written a letter several weeks ago. (X)

Being a "present" tense, the present perfect can be used with "now":

I have now written a letter.

Perhaps this simple explanation can help you Dewi.

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