It As A Preparatory Subject
When the subject is a phrase that includes a gerund, it is used as a provisional subject to begin the sentence. Instead of saying 'Your trying to deceive us is no good', we generally say 'It is no good your trying to deceive us'.
It + verb + subject complement + gerund phrase- It won't be any good my talking to him about it.
- It is no use trying to convince him.
- It was a tough job starting the car with such a weak battery.
- It is no fun having so many children to look after.
- It is just silly throwing away your chances just like that.
It is often possible to replace the gerund with an infinitive.
- It won't be any good for me to talk to him about it.
- It is no use for us to try to convince him.
Some of these sentences can also be rewritten as exclamatory sentences.
- How silly of you to throw away your chances like that!
- What a difficult business it was to start the car with such a weak battery!
When the subject is a clause, the sentence usually begins with it. Instead of saying 'That he was once a terrorist is true', we generally say 'It is true that he was once a terrorist'.
- It does not matter whether it rains or not. (More natural than Whether it rains or not does not matter.)
- It is clear that he overheard our conversation. (More natural than That he overheard our conversation is clear.)
- It is quite evident that you are not really interested in the question. (That you are not really interested in the question is quite evident.)
- It is certain that he left the place in haste. (That he left the place in haste is certain.)
Introductory it is also used with verbs like seem, appear and look when the subject is an infinitive phrase, a phrase with a gerund in it or a clause.
- It seemed strange to see him there.
- It appears possible that the two companies may merge.
- It appeared unwise to offend him.
- It looks improper to behave like that.