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.
They have worked on development-related projects for three years.
I've won three team building awards.
I've helped with the diversification of three financial institutions.
Positive Form:
Subject + have + past participle + (object(s))
He has been developing strong links between the different organizations for five years.
Negative Form:
Subject + have + not + past participle + (object(s))
Alan hasn't donated to any organizations that would qualify his donations as tax deductible in the last year.
Question Form:
(Wh?) + have + subject + past participle + (object(s))
How long have you sought a tax exemption?
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:
They have worked on development-related projects for three years.
I've won three team building awards.
I've helped with the diversification of three financial institutions.
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 Senator doesn't pursue corporate accountability to the community unless he's pressured by his constituents.
The expatriates from Japan don't visit the consulate on Saturdays.
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 World Bank has been destabilizing local economies in developing countries for the last fifty years.
Richard hasn't worked with the disadvantaged population of Birmingham for long.
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.
They have worked on development-related projects for three years.
They have been changing the designated target audience for the last month.
Use 'since' with the present perfect or present perfect continuous to indicate a specific point in time an activity or state began.
George has developed independence despite his disability since the accident.
Jane has been an expert in targeting psychodemograpic categories since the 1970s.
'How long' is used in questions to ask about the duration of an activity or state.
How long have you sought a tax exemption?
How long have you worked on the UFO disclosure project?