1、can/may/must for Speculation
can, may, must can all be used to express speculation, but their meanings and usages differ.
must has the strongest tone, meaning “certainly, must“, and is only used in affirmative sentences. “must + base verb“ indicates speculation about the present situation; “must + have + past participle” indicates speculation about the past. For example:
Mum must be cooking supper now. Mum must be cooking supper now.
He must have finished his work. He must have finished his work.
May/might indicates “perhaps, maybe“. For example:
Tom may go abroad next year. Tom may go abroad next year.
She might have finished the work. She might have finished the work.
He can’t know the answer. He can’t know the answer.
can/could indicates “possibly, will“, and is used in negative and interrogative sentences. For example:
Could she be at home? Could she be at home?
can, indicates a temporary situation, meaning “sometimes…”.
This usage of can is only used in affirmative sentences. For example:
Children are lovely, but they can be tiring.
Training by yourself in a game can be highly dangerous.
2、case Usage Summary
(1) The meaning of the noun case
① means “situation, circumstance“.
If that’s the case, you’ll have to work much harder. If that’s the case, you’ll have to work much harder.
② means “case, instance“.
There were seven cases of cholera. There were seven cases of cholera.
The civil case will be heard in court next week. The civil case will be heard in court next week.
③ means “box, container“.
John bought a case of beer. John bought a case of beer.
(2) Phrases formed with case
①in case means “because something might happen, just in case“, and is a prepositional phrase, often placed at the end of a sentence; it can also be used as a conjunction, followed by a that-clause (that is often omitted), indicating condition or purpose, where the verb in the clause is usually in the form of should + base verb (should is often omitted).
It may rain—you’d better take an umbrella(just)in case(it does). It may rain—you’d better take an umbrella(just)in case(it does).
In case(=If)he arrives before I get back, please ask him to wait. In case he arrives before I get back, please ask him to wait.
He doesn’t dare to leave the house in case(that)he should be recognized. He doesn’t dare to leave the house in case he should be recognized.
②in that case means “in that case, if so“, used to continue from the previous statement.
In that case, you wouldn’t have a pan on fire. You’d have a house on fire! If that’s the case, you wouldn’t just have a pan on fire; you’d have a house on fire.
You don’t like the job? In that case why don’t you leave? You don’t like the job? In that case, why don’t you leave?
He may be late. In that case we ought to wait for him. He may be late; in that case, we ought to wait for him.
③in any case means “in any case, anyway“.
We have to help him to pay the debt in case. We have to help him to pay the debt in any case.
④in no case means “in no case, under no circumstances“, and when used at the beginning of a sentence, the sentence requires partial inversion.
In no case shall I forget the expression on her face. I shall never forget the expression on her face under any circumstances.
⑤in case of sth. means “in case of something happening, if, in the event of“, and is a phrase preposition, followed by a noun, pronoun, or -ing form as the object.
In case of fire, ring the alarm bell. In case of fire, ring the alarm bell.
In case of rain（=In case it rains）,they can’t go. If it rains, they can’t go.
In case of his being absent, we’ll put off the meeting till next week. If he is absent, we’ll postpone the meeting until next week.
⑥in the case of means “as for, regarding“, and is a phrase preposition.
In the case of your debt, I’ll pay it off for you. As for your debt, I’ll pay it off for you.
3、catch fire/ on fire
catch fire means “to catch fire“, indicating an action. on fire means “to be on fire, burning“, indicating a state. For example:
Suddenly a pan of oil catches fire. Suddenly a pan of oil catches fire.
Soon the whole floor was on fire and it was impossible for people on the floors above to escape. Soon the whole floor was on fire, making it impossible for those above to escape.