Which one is correct? Can i use them interchangably and is there a common rule for such constructions? Thanks in advance.
It is an important thing to do contains an example of what The Cambridge Grammar Of The English Language (CGEL, p1255) calls a 'hollow non-finite clause:
In its general introduction to the topic, the CGEL gives these examples (among others):
- The problem took her only a few minutes to solve.
- That he would do such a thing is hard to believe.
- You won't find these kids easy to teach.
According to the CGEL "there are six constructions where hollow to-infinitivals are required or permitted". The second of these constructions are those that "are licensed by an attributive adjective". This construction type matches the sentence in question It is an important thing to do.
Among the examples given are:
- It's a difficult book to understand.
- That wasn't a very sensible remark to make.
- This was a surprising decision for them to take.
The last of these provides the pattern for an alternative to the OP's sentence. Namely the inclusion of the subject:
- It is an important thing to for you (me/him, etc.) to do.
The CGEL does not explicitly rule out the passive in such constructions. But using the passive here makes the sentences more complex than they need to be. And it makes them sound unnatural to me as a native English speaker.
Addendum: A similar question was asked about the first of CGEL's hollow to-infinitivals ('as a complement to predicative adjectives and nouns'). The answer contains a link to Wikipedia's interesting grammatical feature called tough movement.
This question has been taken from Michael Swan' s Practical English usage on page number 273.
Some times there is not much difference between active and passive infinitives when they are used as infinitive complements( to + infinitive or to + be + past participle.)
It is an important thing to do ( active infinitive)
It is an important thing to be done( (passive infinitive)
They are called active and passive infinitives used as infinitive complements.
The active infinitive to do may be
changed to to be done passive infinitive.
to make is changed to to be made
Both the sentences are correct , and mean the same thing
Michael Swan in his Practical English On page number 273 under the title 287 Infinitive complements (5) active and passive infinitive with similar meaning gave this information.
He gave the following sentences
There is a lot of work to do/ to be done.
There are six letters to contact/ to be contacted.
Give me the names of the people to post/ to be posted
The people to interview / to be interviewed are in the next room
According to Michael Swan all the four sentences above are correct and mean the same thing.z
If the answer is wrong, I can no longer depend on his book as it is not being accepted by his fellow country men and native speakers of English and so it is unreliable.