Past to Present
Present Perfect
Present Perfect to Express Past to Present
The present perfect connects an action or state which began in the past and to the present moment in time.
How long have you worked without computer access?
I've outsourced to twelve different contract management companies.
Jane has provided our furnishing since January.
Positive Form:
Subject + have + past participle + (object(s))
Those theme parks have been unsafe since the 1980s.
Negative Form:
Subject + have + not + past participle + (object(s))
We haven't worked from those recipes for very long.
Question Form:
(Wh?) + have + subject + past participle + (object(s))
How long have you worked without computer access?
Present Perfect to Express Duration
When an action begins in the past and continues into the present moment we use the present perfect. This use of the present perfect expresses duration over time FROM the past moment TO the present moment.
Example:
How long have you worked without computer access?
I've outsourced to twelve different contract management companies.
Jane has provided our furnishing since January.
Contrast to the Present Simple
The use of the present simple expresses activities that occurs on a regular basis, such as habits and routines.
Example:
The wholesaler usually ships his products on Mondays.
The production center usually closes at seven o'clock.
In contrast, the use of the present perfect expresses actions that take place over time beginning in the past and coming into the present moment in time.
Example:
The Hilton has offered valet parking for ten years.
I've outsourced to twelve different contract management companies.
Use of 'For', 'Since' and 'How long'
Use 'for' with the present perfect or present perfect continuous to indicate the duration of an activity or state.
Those tour operators have worked at Universal Studios for thirty years.
The Hilton has offered valet parking for ten years.
Use 'since' with the present perfect or present perfect continuous to indicate a specific point in time an activity or state began.
Jane the janitor has cleaned the banquet rooms since 1977.
He has lunched in the employee dining room since taking over the company in January.
'How long' is used in questions to ask about the duration of an activity or state.
How long have you worked with a dietician?
How long have you worked without computer access?