An action expressed ,by the Past Indefinite belongs exclusively to the sphere of the past, while the Present Perfect shows that a past occurrence is connected with the present time.
She is not well and has changedvery much of late.
She changedvery much a great many years ago. (Dickens)
The Present Perfect is never used with such adverbial modifiers of the past time as yesterday, the other day, last week etc. With such adverbial modifiers as to-day, this week etc. both the Present Perfect and the Past Indefinite are used. The tenses are used according to the principle mentioned above (§ 4, § 18).
I have toldyou three times this week that she is coming home for a year.
(Dreiser)
I want your sister, the woman who gaveme money today. (Dickens)
With the adverb just the Present Perfect is used.
I havejust hireda new pianist from St. Joe — a Negro. (Dreiser)
With the expression just now the. Past Indefinite is used.
I sawyou come in just now. (Dreiser)
Just now is less frequent than just.
THE PAST PERFECT
The formation of the Past Perfect.
1. The Past Perfect is formed by means of the Past Indefinite of the auxiliary verb to have and Participle II of the notional verb.
2. In the interrogative form the auxiliary verb is placed before the subject.
In the negative form the negative particle not is placed after the auxiliary verb.
Affirmative
Interrogative
Negative
I had worked
He had worked
She had worked
We had worked
You had worked
They had worked
Had I worked?
Had he worked?
Had she worked?
Had we worked?
Had you worked?
Had they worked?
I had not worked
He had not worked
She had not worked
We had not worked
You had not worked
They had not worked