0 used to show when it is necessary or would be a good thing to perform the activity referred to by the following verb:
If there's any doubt about the rocket's engines, we ought to cancel the launch.
I'm surprised at you behaving so badly - you ought to know better.
Whoever uprooted that tree ought to be ashamed of themselves.
Men and women ought to be able to compete for jobs on an equal footing.
In theory, the journey ought to take three hours, but in practice it usually takes four because of roadworks.
This sauce needs a bit of flavour - I know, some lemon juice ought to do the trick.
Your rash ought to clear up quickly if you use this ointment regularly.