MODALS IN THE PAST FORM

When do we use modals? To talk about someone's ability (or inability) to do something example: "We can find your house without the street plan." "She can't have a daughter that old!" To talk about an action that is necessary (or impossible, or not necessary) example: "You must always have your driver's licence when you are driving your car." "You needn't carry your passport around with you." To talk about a situation that is possible (or impossible) example: "Do be careful with that glass, the baby might knock it over"

A modal verb always has the same form:	There is no past form (-ed), no present participle (-ing) and no 3rd persons singular (-s).
Modal verbs come before the subject in questions:	example: "May I come to your house for tea?"
Negative forms:	Modal verbs have n't or not after them in the negative. example: "mustn't" - "needn't".

PRESENT FORM	PAST FORM
can	could
may	might
will	would
shall	should
must	-
ought to	-
need	-