Pronoun "it" is usually used when you refer to something, for example: It is my home. So, when you say, "It is my home", you can show me which house you refer as "it". However, there are cases when you use "it" when you are not actually refer to anything, you can not show the thing you refer as "it". This is called "Dummy Pronoun". There are three major non-referential uses of the pronoun "it" (as a "dummy pronoun").
a. empty subject
Empty "it" occurs when there are no participants to fill the subject slot. Usually when you refer to weather condition, time, or distance, for example:
- it is raining
- it is five o'clock
- it is a long way from Quebec to Florida.
You can also find "it" as empty objects.
b. Anticipatory subject/object
"it" is inserted as a subject when a clause has been extraposed, for example:
- It would be fun to see a movie after work.
- It is amazing that you are finally married.
c. Subject in cleft constructions
It is found in cleft constructions, when you want to put an emphasize on a particular element in the clause, for example:
- It is the key that you are looking for, isn't it? (means "you are looking for a key, not a pen, right?")
- It is tonight that I will leave. (I will leave tonight, not tomorrow.)
