There are several auxliiary verbs (the ones that help to form a tense or an expression), and some of them are modal auxialiaries (may, must, will, etc). Can is one of the auxiliary verbs used for permission , possibility, ability, etc.In the sentence "We can't go against the law, Doroty.", can't is a word that <em>expresses the idea of not having permission, not being allowed.</em>
