The present perfect tense is used to describe actions that took place in the past and continue to be relevant in the present – and, in some cases, actions that took place in the past and continue to take place in the present.
The simple past tense is used to describe actions that took place in the past and no longer take place in the present. It does not convey the same sense of continuity or relevance as the present perfect.
Here’s an example:
- President Obama has stated his intent to run for a second term of office.
Here, the present perfect is used because the election in which the currently-sitting president will compete has not yet occurred, and so the president’s announcement that he will run is still relevant.
It would not be appropriate to write, “President Obama stated his intent to run for a second term of office,” unless this sentence were situated in a specific context that no longer exists. For example: “On April 4, 2011, President Obama stated in an email to his supporters that he will run for a second term of office.” Here, the simple past is appropriate because the email announcing the president’s intent to run was sent on a day that has ended. Although those who follow the news know that, at the time of this post, the president’s announcement is still relevant and his intent to run ongoing, this is not really important here and should not suggest the use of the present perfect, as the purpose of the sentence is to convey information about events that happened at a specific time in the past – not to imply the continuity of the president’s intent.
Another, perhaps easier example:
- President Johnson stated his intent to only serve one term in office.
Lyndon B. Johnson was president of the United States from 1963-1969 and served one elected term, at the end of which he decided not to run for another. It would not be appropriate to say, “President Johnson has stated his intent to only serve one term in office,” because his intent is no longer relevant (i.e. does not affect events today). There is no upcoming election in which Johnson could or would complete (he died in 1973).
In academic writing, the simple past and present perfect tenses are often interchangeable, as in:
- Lee observed the importance of news media coverage.
- Lee has observed the importance of news media coverage.
In general, the present perfect seems to be more popular than the simple past, but note that when time-specific details are provided, the simple past may be required, as in:
- In 1982, Lee observed the importance of news media coverage in a study that described the effects of TV-watching on adolescent development.
However, you could also write:
- Lee has observed the importance of news media coverage in a study that describes the effects of TV-watching on adolescent development.
And if Lee has conducted further studies on the same topic, you might write:
- Since 1982, Lee has observed the importance of news media coverage in several studies on the effects of TV-watching on adolescent development.
