Even within the same use, different modals convey different ideas and attitudes. It often depends on who is talking. When talking about obligation, for example, it is wrong to always use “must” as must also contains information about who holds authority in a particular situation.
Consider the examples below. Think about their difference in meaning – the questions will help you.
(a) We must have a party to celebrate.
(b) We should have a party to celebrate.
(Both are suggestions, but which speaker is more certain that the party will actually take place?)
(a)You must wipe your feet before entering the house!
(b) You have to wipe your feet before entering the house, don’t you?
(Who has authority here? Who is making the rule - The person saying it or someone else?)
(a) You have studied grammar for 6 years so you must know the rules by now.
(b) You should know the rules by now, but if you don’t, get studying!
(c) You have to know the rules to pass the exam.
(Which sentence expresses an assumption, a necessity which one gives advice?)
Special Uses of Must:
Where would you read/hear these sentences? What does that tell you about some of the uses of must?
· CLOSING DOWN! EVERYTHING MUST GO!
· PASSENGERS MUST NOT CROSS THE RAILWAY LINES. USE THE UNDERPASS
· CANDIDATES MUST BE AT THEIR ROOM AT LEAST 15 MINUTES BEFORE THE EXAM BEGINS
· You must come and have dinner with us this week.
Some Other Situations:
(a) I must buy a new dictionary.
(b) I have to take 2 pills, 3 times a day.
(Which modal is used to express a habitual action?)
(c) Something should be done to stop rising crime!
(d) Something must be done to stop rising crime!
(Which speaker feels more strongly about this issue?)
(e) People caught shoplifting have to be prosecuted.
(f) People caught shoplifting must be prosecuted.
(Which speaker is merely commenting on the obligation and which speaker approves of it?)
