Why didn't we see this before?

[EngLearner]

Source: "The Titan Find", a movie (timestamp: 5m53s).

A couple of operators notice that an unknown spacecraft is on a collision course with their spaceship:

Operator #1: "Sir, I've got something odd here. I've got an approaching craft on an intersect course with Conquered... Can you confirm that?"

Operator #2: "Yeah, it's there. Alright, try to raise them."

Operator #1: "This is Conquered calling a spacecraft approaching from section three. Please identify yourself. You are on a collision course... Please respond. Do you read me?"

Operator #2: "Why didn't we see this before?"

Would it be correct to say: "Why haven't we seen this before?"? If not, why is the simple past "didn't we see" required in this context?

 

[Rover_KE]

They’re both correct.

 

[jutfrank]

I want to say the present perfect is not correct there because that is not what he says. What is 'correct' is surely the form that a speaker uses, since that's what he means. If he uses the past tense, it's because he's talking about the past. By before, he means 'at some point in the past'.

If you change the tense/aspect, you change the meaning. Why would you do that? Study and learn from good authentic natural examples like this but don't alter them. You can ask why he uses the past simple but you can't ask whether a different form, with a different meaning, is 'correct'.

 

[EngLearner]

In "Why haven't we seen this before?", "before" means "before now", i.e. we've just seen it.

In "Why didn't we see this before?", "before" means "before you mentioned it a few seconds ago", i.e. we didn't see it until then.

Would that interpretation be correct in the context given?

 

[jutfrank]

In "Why didn't we see this before?", "before" means "before you mentioned it a few seconds ago", i.e. we didn't see it until then.

Would that interpretation be correct in the context given?

I think that's right, yes.

 

[EngLearner]

If you change the tense/aspect, you change the meaning. Why would you do that?

Because sometimes, according to what I've learned so far, I expect a different tense when there's a certain grammatical pattern. When I came across the past tense in the movie, the following example instantly sprang to mind:

That's a lovely dress you're wearing. Why haven't I seen it before?

I was surprised that the past tense was used in the example from the movie because it seemed to me that it was also possible to express the idea the way it was expressed in the dress example:

That's a ship that's on a collision course with ours. Why haven't we seen it before?

 

[jutfrank]

Because sometimes, according to what I've learned so far, I expect a different tense when there's a certain grammatical pattern.

Well, don't do that. You can't usually tie it to patterns. Focus on why the tense that was used was used.

 

[EngLearner]

You can't usually tie it to patterns.

But I need to tie it to something. I know there are no clear-cut rules, but still there is regularity and logic. I think it's useful to see if one or more tenses are correct under certain circumstances and then to understand why each of them is correct, and why the speaker chose out of them the one he chose.

 

[emsr2d2]

Sometimes more than one tense is perfectly possible. When you see a tense being used and you can't work out why, sometimes we'll be able to explain, but sometimes the only person who can explain it is the writer.

 

[jutfrank]

But I need to tie it to something.

You tie the form (the tense) to the meaning. That's all.

I know there are no clear-cut rules, but still there is regularity and logic.

I don't know what you mean. What regularity? What logic? I don't know what 'rules' you're talking about.

I think it's useful to see if one or more tenses are correct under certain circumstances

What do you mean by 'correct'? The tense that is used is the tense that is 'correct'.

and then to understand why each of them is correct, and why the speaker chose out of them the one he chose.

To my mind, if you're studying real piece of language in use, only one tense can be 'correct'—the one the speaker chose. Each tense has a particular meaning, and it's this meaning you have to think about.

 

[teechar]

I think it's useful to see if one or more tenses are correct under certain circumstances and then to understand why each of them is correct,.

It's not actually that difficult to get a reasonable grasp of tenses in English, and to understand the reasons for their use. The best way to achieve that is to listen to and read a broad range of quality material by native speakers/writers. Read online newspapers, watch current affairs programs, films, and TV series, and listen to podcasts. The more you immerse yourself in the language, the better your understanding of the use of tenses will become.

 

[Rover_KE]

... sometimes the only person who can explain it is the writer.

... and sometime not even then – except to say that's the tense that sounded right at the time of writing.