Photo Diary


Is there any difference in meaning and use between can't have done and couldn't have done?

There is no difference in meaning or use between can't have and couldn't have. They are both used to make deductions or draw conclusions about things that probably did not happen in the past. For example if you are looking for something and can't find it, you might say:

I can't find Jimmy's old audio-cassettes. Where could he have put them? He can't have thrown they away, surely.

Or if you at the station, waiting to meet somebody off a train and they don't arrive, you might say:

They couldn't have caught this train. We can't have missed them.

must have + past participle Similarly, we use must have to make deductions and draw conclusions about things that almost certainly did happen in the past. To use the audio-cassettes and train examples again, we might say:

I can't find Jimmy's old audio-cassettes. He must've put them in the attic. They weren't on this train, you know. They must've missed it.

Here is another conclusion drawn about Tim Henman's recent victory in tennis in Paris:

He must've played really well to win. I wish I'd seen the match.

can't be / must be To draw conclusions that something is certain or highly probable in the present, we use must be in a similar way. In questions we use can be / could be and in negative clauses we use can't be:

You must be Dmytro! How nice to meet you! Tim has told me so much about you.

It must be a nice life to be a tennis coach - out in the fresh air all day, working with young people.

There's somebody at the door. Who can / could it be? It can't be the postman. It's only seven o' clock.

It can't be lunch time already. We've only just eaten breakfast.

You can't be serious about eating lunch now. We've only just had breakfast.

may have / might have + past participle

Note that we can also use may have or might have to make deductions about things that may have happened in the past that we are less sure about. For example, if you are on a mountain walk and your friends do not arrive back at base camp when you expect them, you might say:

They may have taken a different path and will be back soon. On the other hand, they might've got lost.

After some time they do arrive back, but you discover they have taken a difficult path:

That was a stupid thing to do in these conditions. You shouldn't have done that.

may be / might be

In a similar way, we can make deductions about present events that we are less sure about by using may be or might be:

There's someone at the door. It may be Tom. Can you let him in? Where's Anna? ~ I don't know. I haven't seen her today. She might be out shopping.

hope / wish

We use hope to talk about things which we want and which are likely to happen, and wish for things which we want but are more unlikely to happen.

NOTE: When we use wish and talk about states that we desire, we use the simple past tense. When we use hope, we use the Simple Present Tense.

I hope to be a doctor when I finish medical school.

I wish I could fly like a bird.

NOTE: To talk about wishes for things that are happening now, we use the past continuous tense.

I wish I wasn't feeling so sick today.

NOTE: When we use wish about things in the past, we use the Past Perfect Tense. For hope, we use the Simple Past Tense.

I wish I hadn't drunk so much wine last night.

I hope you drank that medicine I gave you.