If you're introducing them to students, then it's a good idea to do that, rather than overloading them with different senses, especially if they have language backgrounds where each use might be done in a completely different way. Ability is a nice easy one to start with and the present and past are easy to contrast and follow the pattern of past tense for past time, whereas with permissiion, the past tense can be used for present or future time, which can cause confusion.