We know that after the modal ought we use the infinitive with to.
And this makes ought different from other modal auxiliary verbs:
You ought to see a dentist.
However, in one of the well-known American English grammar books
the following definition is given:
Ought to is not commonly used in the negative. If it is used in the negative,
the to is sometimes dropped:
You oughtn't (to) leave your keys in the car.
Dear ALAN! I have not met this kind of rule anywhere, so I have four questions regarding this
1) Is the particle to optional in all types of situations?
2) If it is true, does this rule apply only to contracted form of ought not ?
3) Is there any difference between Am.E and Br.E?
4) Also, any difference between formal and informal language?
Could YOU please answer all four questions?