In Past perfect^x, Auxiliaries^x, Difference between^x

Hellow Zewu I'm an English learner from Japan. I am afraid I don't know much about English enough to answer such questions as those you are asking. But allow me to put my two cents worth. First of all, let me define some grammatical terms. In English, people usually say 'subjunctive mood'...

I'm confused..how to use these phrases properly in sentences. I think "before now" is used with present(present perfect) and past (past perfect) tense. Is this correct? What about "by now" ?? I often come across "by now" with auxiliary verbs. "He should be in his office by now." Is "by...