Modal verbs of deduction are used to express an opinion of the speaker based on information that the speaker has.
Example: Sue goes to school in town. Her school finishes at 2.30, but she often stays after school to talk with friends. She always walks to school which takes her 45 minutes.
Now, it’s 3 o’clock. Where’s Sue? Well, she might be at school. She can’t be at home. She must be out of class.
|They must be in Spain by now.||Use ‘must‘ plus the verb when you are 99% (or almost 100%) sure that something is the case.|
|She might come this evening.David may invite Jessica to the match.||Use ‘might‘ or ‘may‘ to express an opinion that you think has a good possibility of being true.|
|Jane could be at work.||’Could‘ is not as strong as ‘might’ or ‘may’. It is just one of a number of possibilities.|
|You can’t be Chinese!||Use ‘can’t‘ to express an opinion that you are 99% sure is NOT true.|
Have a look at the presentation seen in class for more details: