The driver can't have seen the red light.

[Grablevskij]

English Grammar in Use by Raymond Murphy, second edition ISBN -\0 521 43680 X.

Unit 28 (Must and can't).

Ex. 28.3

5.The lights were red but the car didn't stop.

The answer is given: The driver can't have seen the red light.

Strange answer. In other ways it was not possible that the driver saw the light.

I would say that this is a very ill-stated question. How can it be possible that somebody saw that they were red, but the driver can't have seen it.

Must have ignored the lights. Must have failed to see the red light.

But can't have seen sounds strange for me.

Could you comment?

 

[GoesStation]

It's idiomatic English. The speaker believes it's not possible that the driver saw the red lights.

 

[jutfrank]

5.The lights were red but the car didn't stop.

The answer is given: The driver can't have seen the red light.

Yes, that's right.

Strange answer. In other ways it was not possible that the driver saw the light.

I don't know what you mean by In other ways, but yes, that's right. Actually, it's more accurate to say: It is not possible that the driver saw the red light.

I would say that this is a very ill-stated question. How can it be possible that somebody saw that they were red, but the driver can't have seen it.

No, the speaker means the driver didn't see the red light.

Is that clear now?

[cross-posted]

 

[Grablevskij]

No, the speaker means the driver didn't see the red light.
[cross-posted]

Then what is the difference between "The driver can't have seen the red light" and "The driver must have failed to see the light"?

 

[jutfrank]

They mean the same thing. What makes you presume there's a difference?