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[Hong-Hsien, Ke]

Dear tutors:
Recently, I have studied about English grammar. One example in the grammar book, Understanding and using English grammar (Azar), confuses me. It is an exercise for the modals. Here it is.

A: Mrs. Wilson got a traffic ticket. She didn't stop at a stop sign.
B: That's surprising. Usually she's very cautious driver and obeys all the traffic laws. She �must not have seen" the sign.

The meaning of "mustn�t� is equal to the prohibition. Here, the answer in the book is She �must not have seen" the sign. I feel so confused. How we explain that?

Best wishes,
Yu-fen Lu

[rice07]

Hi

Cited a grammar book handy as saying:

In American English, must not is often used when something is not logically impossible, but when there is strong evidence for believing that it is not the case. Compare:

He only left the office five minutes ago. He can't be home yet. (It's logically impossible that he's home.)

She's not answering the doorbell. She must not be at home. (It's not logically impossible that she's home, but it seems pretty certain that she isn't.)

The restaurant can't be open-- the door's locked.

That restaurant must not be any good-- it's always empty.

In British English, can't is normal for both meanings (though some people use must not for the 'seems pretty certain' meaning). Compare:

She walked past without saying 'Hello'. She must not have seen you.(AmE; some British speakers.)

She walked past without saying 'Hello'. She can't have seen you. (most British speakers.)

Note that the contracted form mustn't is rare in AmE.

So, according to your example sentence--She �must not have seen" the sign, it means '她不太可能有看到那個號誌(or 她應該沒有看到那個號誌)' for Chinese(Mandarin).

Hope that helps.

rice

[Hong-Hsien, Ke]

I see. Thanks a lot!

[CP]

Also, I think the grammar book means to say that, in the U.S. at least, if we use "mustn't" at all (and it is pretty rare), we use it to mean "shouldn't" or "had better not", meaning if you do there will be consequences.

You mustn't take your neighbor's bike without permission = You should never take your neighbor's bike without permission; that is wrong.

You could say "She mustn't have seen the stop sign," but usually you would say "must not" rather than "mustn't" to convey the meaning "I doubt that she saw the stop sign."
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