Even the most advanced student of English has trouble mastering our tenses; so do some native speakers. (In eastern Pennsylvania, where I come from, people often use past perfect — I had gone — when they mean simple present — I went.) Simple present (I go), simple past (I went), simple future (I will go) really are simple, mostly. The ones labeled “perfect” are another story.
Perfect, in relation to tenses, refers to time — the past, time completed or “perfected” (from Latin). Somewhere in the sentence, an action takes place in the past, even if the tense is future perfect. In its simplest form, a verb in a perfect tense consists of a past participle plus an auxiliary:
Present perfect: I have gone
Past perfect: I had gone
(Let’s stick with those for now; future perfect is not often used.)
Imagine a timeline, and please pardon my poor digital drawing skills:
Past perfect Present perfect
Past A past moment NOW Future
Simple past indicates that something happened at a particular moment in the past: I came to New York in August to enroll in journalism school.
Present perfect means that something has taken place over a span of time, from a point in the past up to and including the present: I have come to New York to be a great journalist. That’s what you wanted when you came; that’s what you still want, and you’re stil here.
Past perfect is used for an action that took place before another action in the past; therefore there must be two verbs in the sentence, a simple past and a past perfect: I had never thought about going to journalism school until I heard about CUNY’s program. You heard about CUNY at a particular moment in the past; before that, you had never thought about J-school.
Some words can be clues to what tense you need. Before, until and by the time, for example, usually indicate a specific point in time, therefore simple past: Before I came here . . . or Until I came here . . . They suggest that the verb in the other clause should be past perfect: Before I came to CUNY, I had not written much in English.
On the other hand, since referring to time (as opposed to since meaning because) implies a span of time and calls for present perfect: Since he got his TOEFL scores, he has worked much harder on his English. He got his scores at a specific moment in time; has worked refers to his activities in time span from then to now. But: Since (because) his TOEFL scores were good, he was admitted to the program. Simple past in both clauses.
In both present perfect and past perfect, verbs may be continuous or progressive (referring to actions in progress) — in other words, the -ing form. I could just as easily have written Since he got his TOEFL scores, he has been working much harder on his English. Or: Before I came to CUNY, I had been writing mostly in French.
As for future perfect, it indicates an action that will have happened by some future date. Think of the learning outcomes section of a syllabus: By the end of this course, students will have learned how to . . . You haven’t learned it yet, but during the course, you will learn. When the course is over, you will have learned.
And then there’s conditional perfect: I would have passed if I had studied. In this case had studied is not past perfect, but an obviously contrary-to-fact conditional.
Now, a pop quiz: is the following sentence, written by a student last semester, correct or incorrect?
The word ‘refusenik’ has entered English after the 1970s movement of Russian Jews protested anti-Semitism and denied permission to emigrate abroad.
(Pause for thought.)
Wrong. After denotes a point in time, so it should be entered. Or: . . . has entered English since the 1970s movement . . .
Still confused? Come to office hours on Friday afternoons, leave a comment or e-mail firstname.lastname@example.org.