Reminder : We use the present perfect to describe something that happened in the past without being specific about when it happened precisely. (eg. I have been shopping. —> I went to the shops but when isn’t important.)

In order to be more precise about the time or duration of what we are talking about, we can use “for” and “since”.

• “For” is used to describe a duration.

– Affirmative form : Subject + present perfect + for + duration (eg. I have worked for two years.)

– Negative form : Subject + have / has + not + past participle + for + duration (eg. I haven’t worked for two years.)

– Question form : Have / has + subject + past participle + for + duration (eg. Have I worked for years ?)

• “Since” is used to describe a precise time / moment in the past.

– Affirmative form : Subject + present perfect + since + precise time (eg. I have worked since 1998.)

– Negative form : Subject + have / has + not + past participle + since + precise time (eg. I haven’t worked since 1998.)

– Question form : Have / has + subject + past participle + since + precise time (eg. Have I worked since 1998?)