The Present Perfect Tense
S + Has or Have + the Past Participle
Here is a brief review of the form and function of the present perfect tense
The present perfect is used when the time period has not finished :
I have seen three movies this week.(This week has not finished yet.)
The present perfect is often used when the time is not mentioned :
Gerry has failed his exam again.
The present perfect is often used when the time is recent :
Ikuko has just arrived in Victoria.
The present perfect is often used with for and since :
Greg has lived here for 20 years.
Greg has lived here since 1978.