active vs. passive voice

[Lenka]

Cambridge University Press: Common mistakes at CAE (Debra Powell) - chapter 2:

We use active forms of perfect tenses to describe a situation which has changed:
It's really stormy - the roof has blown off!

I don't understand why the (should I write the article here?) active voice was used here (instead of the passive one!). The roof was blown off by the wind, wasn't it? It couldn't have blown off itself! Why was the active form of the verb used, then? Does it have anything to do with the present perfect tense?

Cambridge University Press: English Grammar in Use (Raymond Murphy) - unit 42 (an exercise):

A tree was lying across the road. (it / blow down / in the storm)

I thought that if the active voice was used in the first example (about the roof), it should be used in this sentence as well.
That's why I thought that the correct sentence (formed from the words in brackets) was "It has blown down in the storm.", but the correct answer was "It has BEEN blown down in the storm."

I am really confused now!! Could you clarify it to me, please?

[Casiopea]

Present Perfect: when the event occurred is either unknown or not important. Here it is unknown:

Ex: It is really stormy right now. The roof's blown off.

Perfect Passive: same as above plus, when the agent of the event is unknown.

Ex: A tree was lying across the road. It's been blown down.

_____________
Suggestion
I don't undestand why active voice was used here.

[Lenka]

Present Perfect: when the event occurred is either unknown or not important. Here it is unknown:

Ex: It is really stormy right now. The roof's blown off.

Perfect Passive: same as above plus, when the agent of the event is unknown.

Ex: A tree was lying across the road. It's been blown down.

_____________
Suggestion
I don't undestand why active voice was used here.

Thank you Casiopea, but I think you missed the point of my question (or I didn't understand your exlpanation). I think I know and understand when the (I never know when to write and omit articles... Is it correct here?) present perfect tense should be used but I don't know why the first sentence was told in active, while the second in passive voice.


(Correct my mistakes, please! I am never sure about when to use articles etc. )

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Editing:
I think I should leave he article "the" out, right?

[engee30]

It's really stormy - the roof has blown off!

To me, the phrasal verb 'blow off' is intransitive; therefore you can't say that 'the roof was blown off'.

*****************
A tree was lying across the road. (it / blow down / in the storm)
It has been blown down in the storm.

Unlike with the previous verb, this time 'blow down' is a transitive phrasal verb.
The storm has blown the tree down.
The tree has been blown down in the storm.
___________________________
NOTE:
Bear in mind I'm not a teacher!

[Casiopea]

It's really stormy - the roof has blown off!

To me, the phrasal verb 'blow off' is intransitive; therefore you can't say that 'the roof was blown off'.

*****************

Excellent explanation.

_________
Suggestion
I think I know when (the) present perfect tense should be used.

[engee30]

Excellent explanation.

I should hope so. Thanks.

[Lenka]

It's really stormy - the roof has blown off!

To me, the phrasal verb 'blow off' is intransitive; therefore you can't say that 'the roof was blown off'.

*****************
A tree was lying across the road. (it / blow down / in the storm)
It has been blown down in the storm.

Unlike with the previous verb, this time 'blow down' is a transitive phrasal verb.
The storm has blown the tree down.
The tree has been blown down in the storm.
___________________________
NOTE:
Bear in mind I'm not a teacher!

Hmm... Thanks, Engee... It seems to be the problem of mine.

How do I recognize that "blow off" is an intransitive verb? I know what the expressions "transitive and intransitive verbs" mean but I can't simply recognize if the verb blow off takes an object.

I've tried to search the word in some Internet dictionaries:
=> It is said here (blow off - Wiktionary) that "blow off" means "to fart", which it does not in my sentence, apparently. And yes, you're right - it's considered an intransitive verb here.. in the meaning of "to fart", though.
=> Here (Cambridge Dictionaries Online - Cambridge University Press) it is said the verb can be either transitive or intransitive.
An example sentence is mentioned there: I blew the dust off the books.
Here it is used as a transitive verb. Why? What is the difference between I blew the dust off the books. and The roof has blown off! ? I guess that it has a different meaning, right? To blow off sth (= from what) vs. to blow off.... A I right? How can I recognize it?

By the way, is it impossible to say "The wind blew the roof off."? Why? I know, the reason is that it is an intransitive verb, as you said, but... how can I recognize it? :(

[Casiopea]

A little help with meaning, here. Both examples express the same meaning, but the second one expresses more than just the one meaning:

Ex1: The wind blew the roof off.
Meaning: removed it from its frame

Ex2: The wind blew off the roof.
Meaning 1: removed it from its frame.
Meaning 2: ignored it (idiom) and not applicable to Ex2., didn't do something; e.g., Max blew off the exam. She didn't go.>

[engee30]

Hmm... Thanks, Engee... It seems to be the problem of mine.

Here (Cambridge Dictionaries Online - Cambridge University Press) it is said the verb can be either transitive or intransitive.
An example sentence is mentioned there: I blew the dust off the books.
Here it is used as a transitive verb. Why? What is the difference between I blew the dust off the books. and T[B]he roof has blown off!?

That's the point - to know and be able to distinguish between intransitive and transitive verbs is the key!
The verb itself, blew, can be both transitive and intransitive; but when a particle is added, it changes significantly, and usually becomes a phrasal verb.
I blew the dust off the books. - here, off is not a particle, but forms the prepositional phrase, off the books.

[bianca]

Cambridge University Press: Common mistakes at CAE (Debra Powell) - chapter 2:


I don't understand why the (should I write the article here?) active voice was used here (instead of the passive one!).
*The active voice is usually more direct and vigorous than the passive.
*yes, the active voice (with a definite article)

To me, this is a matter of style.

AV: It's really stormy - the roof has blown off!

PV: It's really stormy - the roof was blown off (by the wind)!.
The latter sentence is less direct, less bold, and less concise than the former.