I am very confused. Unless I am mistaken, I know "it" has to be a noun of some sort, but I am unable to figure out what noun "it" is referring to.
What is "it" in the following sentence:
It is clear that Bob likes doughnuts.
Heres another couple of examples:
It is impossible to fly.
The it in both example sentences is, as noted, a "dummy it" -- that is, this it is not referential,
and thus doesn't have any meaning, because meaning in pronouns is a matter of reference only.
This dummy it (there are several others) is an artifact of a syntactic rule called Extraposition, which works to make sure that "heavy" subject noun phrases (clauses and the like) don't show up
at the beginning of the sentence where they're hard to process, like this unwieldy example:
Instead, Extraposition inserts a dummy it in place of the heavy NP and shifts it to the end,
where it is much easier to process.
Of course, Extraposition is governed by the matrix predicate (in this case be difficult), and some predicates require it, others forbid it, and many allow it under certain circumstances. Like all syntactic rules; nothing new here.
As the the original question -- what is it?
The answer is that it's several things:
In both sentences, It fills in for the subject of the sentence.
In the example "It is impossible to fly," It is substituted for the subject "to fly".
In the sentence "It is clear that Bob likes doughnuts", It anticipates the subject (this time a that clause) "That Bob likes doughnuts".
Answer from the comments:
In the first example "it" refers to "the fact that Bob likes doughnuts."
In the second example "it" is a dummy pronoun and therefore does not refer to anything.
Links for more information on Dummy Pronouns:
