Student or Learner
1- He looks as if he knew the answer = (He doesn't know the answer).
2- He looks as if he knows the answer = (We don't know whether he knows the answer or not).
3- He looked as if he knew the answer = (The meaning of this sentence (whether he knew the answer or not) can only be understood from the context, it may be the back shift both of the sentences 1 and 2).
4- I was taught that we couldn't use a past perfect for a past unreal comparison. That is;
-She looked as if she was rich, but she wasn’t. (NOT … as if she had been rich).
However, I have been searching for this structure, and I have seen people use 'past perfect tense' in this structure. I don't know whom to believe. For this reason, I am asking if past perfect tense is used or not. For example;
-She acts as if/as though nothing had changed between us, but everything has changed.
-She acted as if/as though nothing had changed between us, but everything had changed.
I am sure #1 and 2# are OK but not sure #3 and #4. Could you please explain to me?
To me, she looked as if she had been rich suggests that she was no longer rich at that time, but there were signs of earlier wealth- maybe she was wearing expensive clothes that were worn and a bit shabby, etc.