FORとSINCEを使う現在完了形

現在完了形を使う場合、for + 期間を使ってその期間,を考慮したり、since + 時点を使ってそれが始まった時を考慮することができます。 FORとSINCE は、過去完了形でも使うことが出来ます。SINCE は完了形のみで使え、FOR は単純過去形でも使えます。

For + 期間

for six years, for a week, for a month, for hours, for two hours
I have worked here for five years.

Since +時点

since this morning, since last week, since yesterday
since I was a child, since Wednesday, since 2 o'clock
I have worked here since 1990.

FORを使う現在完了形

She has lived here for twenty years.
We have taught at this school for a long time.
Alice has been married forthree months.
They have been at the hotel for a week.

SINCEを使う現在完了形

She has lived here since 1980.
We have taught at this school since 1965.
Alice has been married since March 2nd.
They have been at the hotel since last Tuesday.