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What is the difference between these two sentences:-

The traffic police has blocked the road for heavy vehicles since last Friday

and

It has been raining heavily since morning.

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closed as unclear what you're asking by Bradd Szonye, Matt Эллен, Kris, tchrist, TrevorD Aug 1 '13 at 18:18

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question.If this question can be reworded to fit the rules in the help center, please edit the question.

    
There are many differences between those sentences, which obscures the point that you're asking about. You may want to choose more similar examples, such as It has rained heavily versus It has been raining heavily. –  Bradd Szonye Aug 1 '13 at 6:29

2 Answers 2

The continuous or progressive aspect expresses an action in progress, and the perfect verb form expresses a past occurrence with present relevance. When combined, they express a past action that continues into the present.

In general, the present perfect progressive form usually indicates an action that is still ongoing, while the present perfect usually indicates an occurrence completed in the past. For example:

It has been raining heavily since morning.

It has rained heavily since morning.

The first sentence implies that the rain has fallen all day long, from morning until the present. In contrast, the second sentence only implies that the rain fell at some time between this morning and now. Furthermore, the first sentence suggests that it's still raining, whereas the second suggests that it stopped some time before now.

However, English isn't as strict about verb forms as some languages, and there are exceptions to the general rules. We sometimes use the perfect progressive for completed actions, as long as they finished – or were interrupted – in the very recent past. Likewise, there's no rule that present perfect always indicates a complete action; we sometimes use it for ongoing or habitual actions too. In those cases, you must consider context to divine the meaning.

This ambiguity turns up in your other example:

The traffic police have been blocking the road for heavy vehicles since last Friday.

The traffic police have blocked the road for heavy vehicles since last Friday.

While you could interpret the second sentence to mean that the police blocked the road for only a short time during the week, most people would use these two sentences interchangeably. That's because of another quirk of the present perfect form: It usually emphasizes that the consequences of an action continue to the present even if the action itself has not.

To see why this matters, contrast the rain and blockade examples:

It has rained heavily since morning.

The traffic police have blocked the road for heavy vehicles since last Friday.

While both of these sentences are ambiguous, you can infer their meanings from context. In both cases, the perfect verb form indicates that the occurrence is still relevant in the present. For rain, it's easy to see how it's still relevant even if it has stopped falling: wet roads, muddy ground, dreary skies, and so on. In contrast, a blockade isn't very relevant unless it's still in place. Therefore, you can infer that the rain has probably stopped, whereas the blockade is probably still in effect.

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Swan in Practical English Usage (p426) states:

The present perfect progressive focuses on the action situation itself, looking at it as a continuous, extended activity. The simple present perfect, on the other hand, looks more at the ideas of completion and present result.

You could say It has rained heavily since morning, but the progessive form places more emphasis on the continuing nature of the rain.

In the case of the road block, the simple perfect is used to indicate that the block was completed last Friday and its present result is that you cannot use the road.

The equally possible:

The traffic police has been blocking the road for heavy vehicles since last Friday

suggests more strongly than the simple form that the police have been continually present throughout the existence of the block.

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