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.
Franz hasn't read and understood the dialog box message in the past twelve hours.
I've tweaked three programs.
Alan hasn't worked with trialware for very long.
Positive Form:
Subject + have + past participle + (object(s))
Tcp/ip has been the standard set of protocols online for nearly forty years.
Negative Form:
Subject + have + not + past participle + (object(s))
Alan hasn't worked with trialware for very long.
Question Form:
(Wh?) + have + subject + past participle + (object(s))
How long have they included that disclaimer on the packaging?
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:
Franz hasn't read and understood the dialog box message in the past twelve hours.
I've tweaked three programs.
Alan hasn't worked with trialware for very long.
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:
How often do you click on adware?
Philip usually uses the help wizard at eight 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:
Franz hasn't read and understood the dialog box message in the past twelve hours.
Alan hasn't worked with trialware for very 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.
He has developed scalable software for five years.
They have worked to defrag the hard drive for three hours.
Use 'since' with the present perfect or present perfect continuous to indicate a specific point in time an activity or state began.
Jane has worked in desktop publishing since the 1980s.
I have retrieved files from employee computers since 2008.
'How long' is used in questions to ask about the duration of an activity or state.
How long have they included that disclaimer on the packaging?
How long have you worked on developing trojan horse software for the underground resistance?