INTRUDOCTORY IT

Introductory it is a word that is used in sentence, not influence the since of a sentence, because the since has been carried by the other element’s sentence.

-When the subject is an infinitive phrase

Structure: It + verb + subject complement + infinitive phrase (real subject)

Ex: It is difficult to know his motive. (= To know his motive is difficult.)

-When the subject is a gerund phrase

When the real subject is a phrase that includes a gerund, it is used as a provisional subject to begin the sentence

Ex: It is no fun having so many children to look after. (= Having so many children to look after is no fun.)

Note that it is possible to change the gerund into an infinitive.
Ex: It won’t be any good for me to complain to the manager.
-When the subject is a clause
When the subject is a clause, the sentence usually begins with it.

Ex:It is required that he should pay the fine. (= That he should pay the fine is required.)

-Introductory it with seem, appear and look
Introductory it is also used with seem, appear and look when the subject is an infinitive phrase, a phrase with a gerund in it or a clause.
Ex: It looked doubtful whether she would come
-Introductory it as an object
It is sometimes used as the object of the verbs think, feel, deem, count, consider, etc
Structure: subject + verb + it (object) + object complement + infinitive phrase/ clause (real object)
Ex: I think it a pity that she could not win.
-Introductory it in questions
The introductory it is sometimes used in questions.
Ex: Who was it that broke the window?