What is meant by "present perfect", "past perfect", and "future perfect" verbs? How can I identify them or know which is which?
For example, what is the difference between the following two sentences: I had a bad day I had had a bad day
Why do people sometimes use the past perfect form of a verb when the past would suffice? (e.g. “you had mentioned”)
I noticed that my American friends tend to use the past perfect form when they use the verb mention in its past form, almost despite of the context of the sentence. I hear them say "you had ...