'it' confusing me in some sentences

[Harsh Chowdhary]

Hello everyone,
I have one question regarding the use of 'it'. I know that 'it' is used as a pronoun. But sometimes 'it' is used without referring to anything. E.g:-
'it rained last night'
Here it is not referring to anything.
now, let me make make a comparison between following two sentences:-
'The book is worth reading'
'It's worth reading this book'
Both the above sentences are correct but in the second sentence what does 'it' refer to? And lots of examples are there where 'it' is used without referring to anything. Please anyone take the responsibility of explaining this to me in details. Alan and Torsten are specially requested to clear my concept regarding the use of 'it'.

Thank you in advance

[Alan]

Hi,

'It' as used in your sentences is known as an 'anticipatory device' because it introduces the idea that follows in the sentence. And of course 'it' is used in impersonal passive forms as: It was decided to delay the meeting for another week.

Alan
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