What is the grammatical explanation for an 'It looks like ...' clause? (dummy subjects)

Recently, I have been trying to understand the nuances of language to turn myself into a better writer. This has led me to the 'dummy subject' or 'dummy pronoun.' I am clear on the function of 'there,' but 'it' has proven to be more confusing.

I am aware of this subject being used to talk about time, weather, and distance. I am also aware of its use in expletives (changing the position of the subject). However, I can't seem to grasp this sentence construction: 'It looks like ....' An example of what I mean is 'It looks like we've won' or 'It looks like they've gone home.'

To me, the use of 'It' at the beginning of the sentence seems to be a dummy pronoun, as I can't figure out what else it could refer to. Does anyone know the exact grammatical explanation for this?

Solution 1:

The rule is called Extraposition.
It applies to a sentential subject -- an infinitive clause or a that-clause, for instance:

• For him to leave early would be a good idea. (infinitive clause subject)
• That he left early was surprising. (that-clause subject)

Extraposition moves those heavy subjects to the end of the sentence, where they are easier to process, and leaves behind a dummy it to (pretend to) be the subject noun phrase. That produces the kind of sentence English likes - starting with a simple subject (preferably a pronoun), followed by a simple verb (preferably an auxiliary verb), with all the complicated stuff piled up at the end.

• It would be a good idea for him to leave early. (Extraposed infinitive)
• It was surprising that he left early. (Extraposed that-clause)

Whether Extraposition can apply or not is governed by the predicate of the main clause;
be a good idea and be surprising are both predicates that allow it.

Often, as with verbs like seems or looks like, Extraposition is obligatory; the ungrammatical

• *That he left early seems
• *That he left early looks like

Extrapose to

• It seems (that) he left early. (that is optional)
• It looks like (*that) he left early. (that is not allowed)