11.3. Vocabulary. Discuss the difference (if any) between the following sentences.

You could meet your future wife in the club. / You managed to meet your future wife in the club. The first example is definitely not the past. It refers to the future only. The second is the same as ‘can’ in the past, but refers to a single action.

Can you get me another gin and tonic? / Could you get me another gin and tonic? Basically the same, although ‘could’ is perhaps a little more polite.

Will you be able to come back tomorrow? / Could you come back tomorrow? Again little difference. The first is for ‘ability’. The second a polite request to come back tomorrow.

They can’t be French. / They mustn’t be French. The first is for deduction, and someone is speculating that someone is French. The second is plain bad English, and doesn’t make sense. ‘Mustn’t be..’ means ‘don’t be…’ and is only used for prohibition. Not deduction. Always remember that for deduction, the negative of ‘must’ is ‘can’t’.

Did you manage to get the tickets for me? / Could you get the tickets for me? The first is in the past; the second hasn’t happened yet as it is in the future.

We are so glad that you could come. / We are so glad that you can come. The first is probably what you would say after a party has finished and someone is leaving. The second is what you would say when someone accepts your invitation. (For a party in the future.)

He can’t have seen her. / He can’t be seeing her. / He can’t see her. / He could see her. In the first he is looking, he is at the place, and we are deducing that he hasn’t seen her. / The second example is completely different. ‘See’ is not usually used in the continuous form unless it refers to a romance between two people. The meaning is thus ‘it is impossible that he is having a relationship with her.’ / The third means that ‘he is unable to see her’, and refers to the present moment. / The fourth is the past of the previous example, or, it means that there is the possibility that he might see her in the future.

You can’t be telling the truth. / You can’t tell the truth. / You could tell the truth. The first is in the continuous because it is talking about this present moment. / The second could mean ‘you are a liar and incapable of telling the truth’ or that ‘you mustn’t tell the truth’ (i.e. an order). / The last example means that there is the possibility that you may say the truth.