Modal Verbs help you talk about different levels of ability, possibility, certainty and permission. If you need to be able to tell someone what they mustn’t do or what they needn’t do you should also be able to use ought to and have to correctly.
Most modals don’t have to after them. The page Use of modals with to will tell you about those that do have it. Used to is one of those that has it, and it is explained in detail in the Difference between use to and used to. Its companion page explains the difference between the often confused Used to and Get used to. Used to is looked at further in the Difference between used to and would for past habits.
Mustn’t and needn’t are not the same. Really. Honest. No kidding.
Another pair of modals that are often confused are clarified in the Use of have to and must.
Modals seem to be confused in pairs. Our final pair is When to use could and able to. Could as a single being makes one final appearance in You can’t say could of.
Many modals only have small differences in meaning and for that reason can cause confusion. Take a look at my list of commonly confused modals and see which of them often confuse you:
