As If / As Though + Past Subjunctive

One of the uses of the past subjunctive is after as if/ as though to indicate unreality or improbability or doubt in the present. 

  • He behaves as if she was the boss here. (But she isn't the boss or  we don't know whether she is the boss or not.)
  • He talks as though he knew who Jane was. (But he doesn't know or we don't know whether he knows or not.)
  • He looks at me as if I were guilty. (But I am not guilty.)
     

There is no difference between as if and as though.

The verb preceding as if / thoughcan be put to a past tense without changing the tense of the subjunctive:

  • He talks/talked as though he knew who Jane was.

After as if / thoughwe use a past perfect when referring to a real or imaginary action in the past:

  • He talks about Rome as though he had been there himself. (But he hasn't or probably hasn't or we don't know whether he has or not.)

Again, the verb preceding as if / thoughcan be put into a past tense without changing the tense of the subjunctive:

  • Her eyes look/looked as if she had been crying.