Clauses of comparison may be introduced by conjunctions as, like, as if, as though, than; correlative conjunctions as... as, so... as, as... as if.
Swithin’s pale eyes bulged as though he might suddenly have been afflicted with insight.
He spoke as timidly as if he were afraid of me.
An adverbial clause of comparison may correlate with adverbs in the comparative degree in the principal clause. In this case the clause refers to the predicate with its adverbial modifier. Thus in the sentence Mr. Direct’s broken wrist healed sooner than he desired the subordinate clause characterizes the predicate group healed sooner through comparison. The conjunction than is correlated with the adverb in the comparative degree sooner.
The indicative form can also be used.
They don’t have long intervals like they do at other theatres.
The difference between the use of as and like is important. As implies the idea of identification, as in: Let me speak to you as your father ought to (= I am your father and I am speaking to you in that character), whereas like implies the idea of mere comparison, as in: Let me speak to you like a father might (= I am not your father, but I am speaking in the way your father might).
The conjunctions as if and as though may also introduce appositive and predicative clauses, as the comparative meaning may combine with different syntactic connections.
She had a look as if she had something in her mouth.(appositive clause)
She looked as if she had something in her mouth. (predicative clause)
She looked at me as if nothing was wrong. (adverbial clause)
Clauses of comparison sometimes have inverted word order.
He was as obstinate as were most of his relatives.
Special mention should be made of cases when two subordinating devices are used to introduce a clause, usually a conjunction and a conjunctive word: than whose, than which, than where, or two conjunctions: than if. They bear double relation to the main clause, one of which is that of comparison.
He is never more present in my work than when no image of him is there. (comparative and temporal
The butler took his tip far more casually, far more naturally than if Dicky had offered to shake hands with
him. - чем если бы Дикки протянул ему руку (comparative and conditional relation)
The complex sentence with an adverbial clause of condition