Here is the second set of modals.
These modals express degrees of logical force or social expectation.
must/ had better/ should/ ought to
Note that none of them has a past tense or weakened form.
The first one, "must" indicates logical or social necessity.
It expresses the strongest logical or social force.
The modals "should" and "ought to" assert that something is probable or expected, but not necessary.
The modal "had better" expresses advisability.
In other words, if someone "had better" do something, they should do it or there may be negative consequences.
Therefore, "had better" has the feeling of a threat, as in "You had better be there."
This isn't the same as "You should do it," which means you are expected to do it, but without an implied threat if you don't.
One interesting rule is that no more than one modal can be used with any verb.
There are no exceptions to this rule.
Therefore, it's incorrect to say: "He will must be there."
To avoid breaking this rule, there are other words that have the same meaning, but are not modals.
In the case of "must", for example, we use "have to" as in "He will have to be there."
Similarly, we cannot say "He may can come."
Instead, we say "He may be able to come."
One last thing to note about modals.
They use the same form regardless of what the subject is.
If the grammatical subject is l, it, we or they, we use the same form, will.
We would never say "He wills be there."
But with non-modal forms, such as "have to" we must change the form to match the subject.
"He has to be there" and "I have to be there".
(The modal "may" shows that the speaker thinks something is possible.）
（The modal "must" expresses logical or social necessity )
（What must we do has the same meaning as what do we have to do.）
（Tom must be taller than Sue because he is taller than Ben and Ben is taller than Sue.）
（The expression "be able to" has the same meaning as "can"，but it is't modal.）
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