Modals of obligation

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modal verbs of obligation

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Firm obligation or necessity: "must" & "have to"

1. Present obligation: Must and have to both express necessity, but must is generally more formal or urgent. Examples:

• You must see a doctor at once! (urgent necessity)
• I have to be at school tomorrow at 8 a.m. I have an exam!

2. Past & future obligation with "have to": Must lacks past and future forms, so have to is used instead. Examples:

• I had to see a doctor because I felt very sick. (past)
• We will have to study tomorrow. (future)

Certainty or strong probability: "must" and "have to"

These verbs can also show strong certainty about something. Examples:

• He must be over eighty; he was born in 1930. (strong belief)
• If my brother's not in London, he has to be in New York. (certainty about a likely place)

Supposition with "Must Have"

Used to make assumptions about past events, expressing what the speaker thinks certainly happened. Examples:

• I can't find my laptop; I must have left it on the train. (supposition)
• If they're out, they mustn't have heard the news.

Important: "Had to" vs. "Must have"

• "Had to" shows past obligation (e.g., They had to go to London = they were obliged to go).
• "Must have" expresses strong belief about a past event (e.g., They must have gone to Chicago = I think they certainly went).

Informal Use of "Got to"

In informal contexts, especially in spoken English, have to can be accompanied by got in the present tense. Examples:

• We’ve got to hurry; we’re late!
• He’s got to get me a new computer; he broke mine.

Note: The auxiliary verb "have" is almost always contracted in speech (e.g., They've got).

Negative Contexts: "Must not" vs. "Don’t have to"

Must not and don’t have to have different meanings:

• Must not: shows prohibition (e.g., They must not go to London = They are forbidden to go).
• Don’t have to: shows absence of obligation (e.g., They don’t have to go to Chicago = They don’t need to, but they can if they want).

Recommendation or Moral Obligation: "Should," "Ought to," and "Need to"

These verbs are used for giving advice or expressing moral obligations.

1. Should and Ought to Should and ought to are nearly synonymous. They express advice or recommendations and exist only in the present and present perfect forms. Examples:

• You should stop smoking. (recommendation)
• It’s raining hard; the children ought to come indoors. (suggestion)
• If you'd wanted to succeed, you should have worked harder at school. (regret/advice about past)

2. Need to Need to indicates a strong recommendation. Needn’t or don’t need to indicate that something is unnecessary. Examples:

• I’ve been working for hours; I need to take a rest. (strong recommendation)
• Thank goodness, I haven’t got COVID, so I don’t need to stay home. (absence of obligation)

Note: "Needn’t" is never followed by "to" (e.g., I needn’t go instead of I needn’t to go).