Practical English Usage and the Cambridge Grammar of English say that the present perfect “is connected in some way with the present.”
Neither book explains this, and this is why I’m asking for you to indicate how the present perfect “is connected in some way with the present” in the examples below — by saying, for example, “The past is connected with the present in ‘She has lived here all her life’ ... (your answer).”
It is called the present perfect as it uses the present tense of “have” as an auxiliary.
It is a form of the present tense that ends as soon as it is spoken or done.
She has lived here all her life. = She is, as I speak, currently in a state of living here (and she has been in that state all her life.) The second main clause is irrelevant to the tense.
If, on turning round to look at her, the speaker find she is dead, he would have to correct the sentence to “She [had] lived here all her life” as the matter is now in the past. - = She was, when I spoke, then in a state of living here.
He has finished his homework. = He is, as I speak, currently in a state of having finished his homework.
We have been to Canada. = We are, as we speak, currently in a state of having travelled to Canada.
She has forgotten her folder. = We are, as we speak, currently in a state of having forgotten her folder.
If you ask “Well why are we using “have”? It is because, at a very base level, the subject is in possession of the state described.
Your problem comes with:
A: “Have you ever worked for that company?”
B: “Yes, I have worked for the firm, but that was 4 years ago.”
This arises because it is normal to answer, where possible, by using the same form of the verb:
A: “Did you ever work for that company?”
B: “Yes, I worked for the firm, but that was 4 years ago.”
So, where is the connection with the present? A was asking about B’s past experience, which is still currently valid, and so, whilst the present perfect is valid, it is not the only option.
“Yes, I have worked for the firm, but that was 4 years ago.” = Yes, I am, as I speak, in a state of having worked for the firm.”
In Old English, in common with other languages, the verb “to be” was used to form the past tense of verb that described motion or change – some forms of this still exist, but are rare.
“The prisoner is not there! He is gone!”
“You cannot cross the river, the ice is melted.”
They describe a state and it is hard not to see “gone” and “melted” as adjectives. Adjectives describe attributes – and we see that being in a particular state is an attribute.