The key to understanding how English tenses work is realising that just three aspects determine which tense is most appropriate in any given situation. These aspects are:
1. Point of reference (PoR)
2. Special period of time (SpPoT)
The first aspect refers to the time frame that the action of a verb is anchored in, which can be the Past, the Present, or the Future. For example, actions that have a past moment in time or past period of time as their PoR have to be expressed in a Past tense. The PoR can be stated explicitly or be implied in the statement.
Queen Victoria died in 1901.
(Explicit PoR, 1901 is definitely terminated in the past.)
My mother met Queen Victoria.
(Implicit PoR at some time in the definitely terminated past, since QV has been dead for 100+ years.)
My gradfather was a teacher.
implies that my grandfather’s being a teacher happened at a time (or during a time) that is definitely terminated in the past: maybe he retired some time ago or he died some time ago.
Statements that are anchored in the Present can, for example, characterise a person or thing as such, as in
My father is a teacher.
which is a statement about him as a person, and the action of the verb is seen as taking place within the whole time frame of the Present (which is a kind of period of time). What happens, though, if a statement refers to a different period of time—one that, as seen from the PoR, extends into the past? Well, this special kind of period of time means we have to use a Perfect tense. Depending only on whether the PoR is in the Present or in the Past, this will then be a Present Perfect or a Past Perfect tense. Take a look at a couple of examples:
Have you seen the new Bond movie?
I have never been to New Zealand.
We have been friends for ten years.
All of these statements are anchored in the Present, in that their PoR is now; the action of the verb takes places (or, in these examples, has taken place) during a period of time that extends from some point in the past to now. The same thing happens if the PoR is located in the Past, but we are still talking about the action of the verb happening during a period of time that extends from some point in the past to the PoR:
He had been a politician for ten years when he became mayor in 1990.
He had already written five major novels when he won the Pulitzer Prize.
Lastly, what is important to see here is that our focus in each of the above four examples is on a state of affairs (or a person’s state of mind) at the PoR. That’s why we have to use one of the straight Perfect tenses. If, on the other hand, our focus is on the continuous action of the verb over the period of time, we’ll want to use a Perfect Continuous tense:
I have been waiting at the station for 45 minutes, but there is still no train.
John had been living in London for almost five years before he finally became a British citizen.
If we want to express that some action is/was in the process of going on at a particular moment in time (or over a non-special period of time), we also use a continuous tense:
I am reading a play by Shakespeare.
Usually I teach French, but this week I am teaching History.
I was crossing the street when a bomb went off.
The idea of something continuously going on over a period of time is fairly simple to understand, as in the second example above (“this week I am teaching History”). But how can something be going on at a moment in time? Well, if the action of the verb started before the PoR and continues, or would have continued, after it, then it is continuous. In the first sentence above, I am still in the process of reading the book—I started some time ago and will continue reading it for a while. In the third sentence, I would have continued crossing the street if I hadn’t been killed by the bomb blast. At both PoRs, something is going on, and that’s what is in the speaker’s focus.
Note how the tenses are formed in exact accordance with our three aspects (PoR, SpPoT, Focus): if I want to make a statement about Sally’s driving her daughter to football practice every Monday, I proceed as follows. Firstly, the action of the verb is anchored in the Present (i.e., I need a Present tense); secondly, the action of the verb is located squarely within the Present, not within a special period of time that only extends to the present moment (i.e., no Perfect tense); and thirdly, my focus is on a certain state of affairs, not on the continuous action of the verb over the period of time (i.e., no continuous tense). The result is: I need to use the Simple Present tense and say:
Sally drives her daughter to football practice every Monday.
If, after a two-hour absence, I want to ask my children about their activities during that absence, I have to use a Present tense because my PoR is now; a Perfect tense because the action I want to ask about is located in a special period of time that extends to my PoR; and a Continuous tense because my focus is on the continuous action of the verb over the period of time, not some state of affairs at the PoR, making a Present Perfect Continuous tense:
What have you been doing?
If, however, after a two-hour absence, I arrive home and one of my children is sitting on the kitchen table with a knife sticking out of this thigh, something changes. My PoR is still the same, and so is the special period of time during which the action of the verb has happened; but my focus is now definitely on a certain state of affairs. So I would probably ask:
What have you done?
And finally, all the above considerations are valid with PoRs in the Future:
He will be mayor one day.
(Statement about a state of affairs.)
I hope the sun will be shining when I get off work tomorrow.
(Something going on at future PoR.)
Next week we will have known each other for exactly ten years.
(Future PoR, action of verb located in SpPoT, focus on state of affairs.)
This time next month, I will have been living with you for exactly one year.
“Signal words”: Certain words are sometimes said to “signal” that you should use a specific tense. For example, “just” and “now” are supposed to be signal words for the Present Continuous, “ago” for the Simple Past, “never” and “since” for the Present Perfect. Consider the following sentences:
Tom lived in a remote Swiss village all his life, so he never saw the ocean.
I have just finished my final exam. I am a teacher now.
I haven’t seen her since about two years ago.
Do yourself a favour and forget everything they taught you about “signal words”. They’re bullshit.
It’s all about whether the action of the verb is terminated: Most teachers will tell you that the decision whether to use, for example, a Simple Past tense or a Present Perfect tense depends on whether the action of the verb is terminated. That is wrong, as you can easily see from these examples:
Have you seen the new Bond movie? – Yes, I have. I saw it last Saturday.
(“I have” refers to the same action but a different time frame as “I saw it”.)
Queen Elizabeth was the Queen of England in 1990.
(QE still is the Queen of Enland; what is terminated is only the time frame referred to.)
“Systematics of the English Tenses” by Peter Monnerjahn is licensed under a
Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.