ANSWER: Hm. You’re asking as if I had all the answers!
This question was posted on my community forum. The student wondered if we could say both “as if you didn’t know me” and “as if you don’t know me.” I felt stumped. Was the use of a present verb form incorrect? In an imaginary conversation in my head, it sounded natural: “Why are you looking at me as if you don’t know me?”
Could it be that both forms are acceptable, but one is limited to informal conversation? This would be similar to encountering the use of the simple past was in place of the past subjunctive were in unreal conditional sentences: “He’d be a good dance partner for you if he were (was) just a bit taller.”
In any case, I immediately felt that verb forms after as if and as though weren’t limited to the past subjunctive. Do you agree? If so, then please help me list all the possibilities.
1. Past subjunctive. We all agree on this one. This is the verb form textbooks like to use in their examples with “as if”: She walked into the room as if she were royalty. We know that we can also change the verb in the main clause to a present form and the past subjunctive remains correct in the adverb clause: She walks into any room as if she were royalty. (Verified or likely fact: She is not royalty.)
2. Infinitive. In my initial response to the student, I gave this example: She never broke the silence, but she looked at me as if to say, “I’m sorry.” Later, I was happy to see that Biber et. al confirmed the use of the infinitive (what they call a to-clause) after as if (841).
3. Present participle. A colleague reminded me that participles also appear after as if and as though. Biber backs up her claim, at least with the present participle (840). Let’s consider this sentence: With great excitement, the child watched the movie and swung his arms as if fighting his own battle against pirates. That works, right?
4. Past participle. Is this possible? I can’t find a written source to confirm this structure, but my clever colleague supplied a good example. I then created a similar one: The grandfather stood as though baffled by his grandchildren’s behavior. It sounds correct to my ears. How about yours?
Could we explain that the examples with participles are really reduced adverb clauses that originally made use of the past subjunctive? In other words, “as if fighting” = as if he were fighting and “as though baffled” = as though he were baffled.
One thing we can point out to students is that although there is variation in the use of as if and as though, the meaning is often contrary to fact. Also, these adverbial subordinators of manner are used across registers, but they appear most often in fiction (Biber 842).
Biber, D., et al. 2002. The Longman student grammar of spoken and written English. London: Longman.