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.
Our generals have preferred diplomacy over military intervention since the conflict broke out in January.
I've compiled three reports on the technical assistance NGO.
How long have you worked on the UFO disclosure project?
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))
Richard hasn't worked with the disadvantaged population of Birmingham for long.
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:
Our generals have preferred diplomacy over military intervention since the conflict broke out in January.
I've compiled three reports on the technical assistance NGO.
How long have you worked on the UFO disclosure project?
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:
Phillip usually focuses on issues involving ethnicity.
Philip usually abhors workplace violence on Mondays.
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:
I've compiled three reports on the technical assistance NGO.
They have been involved in development activities for only six months.
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 involved in development activities for only six months.
Use 'since' with the present perfect or present perfect continuous to indicate a specific point in time an activity or state began.
Our generals have preferred diplomacy over military intervention since the conflict broke out in January.
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?