Editor Emily Brewster outlines the use of the present perfect verb tense.
The present perfect is used mainly in four situations. They are as follows:
1. to talk about activities or states that began in the past and are completed at the time of speaking:
"I have fixed the radio."
This sentence means that I started to fix the radio earlier but have only now completed that job.
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2. to talk about past activities that have a result in the present:
"This evidence has influenced our decision."
This sentence means that evidence encountered in the past is influencing the decision we're making now, in the present.
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3. to talk about events that have just happened:
"We've eaten dinner."
This sentence means that we recently ate dinner.
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4. to talk about events that happened at an unspecified time before now:
"I have read that book."
This means that I read the book being talked about at some time in the past.