Scientific English as a Foreign Language
Answers to Lesson of September 25, 1998
Simple Past and Present Perfect Verb Tenses

Today's topic is the difference between the simple past and present perfect verb tenses. The difference is very important in English. The two tenses are important in scientific writing because most of the work we describe takes place before we write about it.

"When I was at the National Renewable Energy Laboratory, I worked on semiconductors," is an example of the SIMPLE PAST tense. My work at NREL is over. It was completed some years ago. Simple past is used for actions that occured in the past and that are over.

"At the Swiss Federal Institute of Technology, I have worked on the nanomechanical properties of materials," is an example of the PRESENT PERFECT tense. I started my work some years ago, but continue it. Most scientific publications are written in the present perfect because you start your work in the past and continue it into the present and perhaps into the future.

There are two more variations on the use of present perfect. One is where the present perfect refers to an event that just happened. "The Starr report has appeared on the Internet," is an example. Yes, it is an event in the past, but if I were to say "The Starr report appeared on the Internet," it would seem less timely. The present perfect emphasizes the newness of the event.

Past events that repeatedly occur into the present are also described by the present perfect. "Scientific American has arrived at our house for many years."

In the sentences below, would you use the simple past or the present perfect?

1. Yesterday I went to the movies.
2. Did you hear? Kohl has won the election!
3. Our continuing work has shown that the molecules obey the worm-like chain model.
4. Last year's work showed that the molecules obey the worm-like chain model.
5. My Scientific English lessons have arrived almost every week since I first subscribed.
6. When I was a subscriber, my Scientific English lessons arrived almost every week.

Twas the night before implementation and all through the house,
not a program was working, not even a browse.
The programmers hung by their tubes in despair,
with hopes that a miracle soon would be there.
The users were nestled all snug in their beds,
while visions of inquiries danced in their heads.
When out in the machine room there arose such a clatter,
I sprang from my desk to see what was the matter.
And what to wondering eyes should appear,
but a super programmer (with a six-pack of beer).
His resume glowed with experience so rare,
he turned out great code with a bit-pusher's flair.
More rapid than eagles, his programs they came,
and he cursed and muttered and called them by name.
On Update! On Add! On Inquiry! On Delete!
On Batch Jobs! On Closings! On Functions Complete!
His eyes were glased over, fingers nimble and lean,
from weekends and nights in front of a screen.
A wink of his eye and a twitch of his head,
soon gave me to know I had nothing to dread.
He spoke not a word, but went straight to his work,
turning specs into code; then turned with a jerk.
And laying his finger upon the "ENTER" key,
the system came up and worked perfectly.
The updated updated; the deletes, they deleted,
the inquiries inquired, the closings completed.
He tested each whistle, and tested each bell,
with nary a bomb, and all had gone well.
The system was finished, the tests were concluded,
the users' last changes were even included.
And the user exclaimed with snarl and a taunt,
"It's just what I asked for, but not what I want!"

- Anonymous

Back to the index page.

Created September 25, 1998, by Nancy Burnham and Fred Hutson.