You must have a good understanding of basic modals in terms of their expression. These slides mainly talk about modals of necessity and certainty in all tenses.

1. ESL: Advanced Grammar
Instructor: Dustin French

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Modals are auxiliary verbs (helping verbs) and do not follow the
rules of conjugation as regular and irregular verbs.

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Unit 5 –Modals of Necessity
Simple Modal (present and future)
modal + base form verb

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Perfect Modal (past)
modal + have + past participle

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Modals of Necessity…
Some modal verbs
Can Could Had better
May Might Must
Ought to Shall will

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Must, Have to, Have got to
Must
To show very strong obligation that can’t be ignored.
Have to
Used in all forms and situations (formal and informal)
Have got to
Used in informal conversations. Rarely used as a negative

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WARNING!

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Negative: Must vs. Have to
must + not
To prohibit in a much stronger feeling
don’t / doesn’t + have to
To do something that is not necessary

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Should and Ought to
• They both express ‘advice’.
• ‘Should’ can only be expressed in the negative
and be used in a question.

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Past: Should/Ought to + have
• To express advice about past situations.
• The action did not happen (it’s too late).
In past negative, the action happened.

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Be supposed to
• To show expectation.
• Used only in the present and past.
• The action didn’t happen in the past affirmative.
• The action happened in the negative affirmative.

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Unit 6 –Modals of Certainty
Speculations about the present modal + be
Speculations about the past modal + have + been
Speculations about the future modal + base verb + time

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Must, Have to, Have got to
• Speculating about the present.
• The speaker is almost certain.

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May, Might, Could + base form
• Speculating about the present.
• The speaker is less certain.

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Must have/Had to have + Past part.
• Speculating about the past.
• The speaker is almost certain.
2. She must have helped him.
3. They must have studied well.

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May/Might/Could + have + Past part.
• Speculating about the past.
• The speaker is less certain.

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Should / Ought to
• Speculating about the future.
• The speaker is almost certain.

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May, Might, Could + base form
• Speculating about the future.
• The speaker is less certain.