An English teacher in Iran, Farhad H., sent me this grammar SOS a few days ago:
“Figuring out the difference between the present perfect and the present perfect continuous is driving me crazy. In particular, how do the two statements below differ in sense?
“(1) ‘Peter, sorry for my slow reply! My computer and telephone have not been working for two days. I apologize for the bad behavior of both devices.’
“(2) ‘Peter, sorry for my slow reply! My computer and telephone have not worked for two days. I apologize for the bad behavior of both devices.’”
My reply to Farhad H.:
To understand how Statements 1 and 2 differ in sense, let’s first do a quick review of the present perfect and the present perfect continuous.
The present perfect tense indicates (a) that an action was completed—finished or “perfected”—at an unspecified relatively recent time before now, or (b) that an action that started in the recent past extends to the present. This tense has the form “has/have + past participle of the verb,” as in “They have pursued that alternative” (a done thing) and “They have pursued that alternative for six months now” (the action is still ongoing).
Since the present perfect indicates an action that happened at an unspecified time before now, this tense can’t use specific time expressions like “yesterday,” “last week,” or “last year.” We can’t say “She has loved me yesterday.” However, the present perfect works with nonspecific time expressions like “once,” “many times,” or “never,” as in “That scenario has been repeated many times.”
In contrast to the present perfect, the present perfect continuous indicates (a) that a continuing action was completed at some point in the recent past, or (b) that a continuing action that started sometime in the recent past continues up to the present. This tense has the form “has/have + been + present participle (the verb ending in -ing),” as in “She has been reading just now” (a done thing now) and “She has been reading without letup” (the action is still ongoing).
The present perfect continuous, unlike the present perfect, can use specific time expressions like “for three hours,” “for half a day,” and “since last month,” as in “The starving Kidapawan farmers have been waiting for food relief for several days.” Since the present perfect continuous has the general sense of “lately,” it often uses the words “recently” and “lately” to emphasize that sense, as in “Popular TV shows have been bursting with political advertising lately.”
Now let’s closely examine Statement 1: “Peter, sorry for my slow reply! My computer and telephone have not been working for two days. I apologize for the bad behavior of both devices.” Its second sentence, “My computer and telephone have not been working for two days,” is clearly in the present perfect continuous, with the sense of a continuing situation that started sometime in the recent past and continues up to the present. The use of the specific time expression “for two days” indicates that the condition continues up to now.
As to Statement 2, its second sentence, “My computer and telephone have not worked for two days,” isn’t really in the present perfect tense as you evidently presumed. Indeed, its use of the specific time expression “for two days” makes it grammatically defective. With that time expression, that sentence should be in the simple past tense instead: “My computer and telephone did not work for two days.”
I think the discussion above has made the difference very clear between the past perfect and the past perfect continuous. It is therefore likely that what was driving you crazy figuring out that difference was your use of a grammatically defective present-perfect sentence to distinguish its sense from that of its present perfect continuous counterpart.
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