流利说 L6-U2 P2 Learning

Talking about Modals 2

Here's the second side 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 some 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".