III. DESCRIPTIVE/INTERPRETIVE FUNCTION OF MODALS: DESCRIPTIONS FROM THE SPEAKER'S POINT OF VIEW (OPINION)

4. Modals of Ability

4.2 Multiple Functions or Meanings are Possible

A single modal often expresses more than one social or practical function. Though a modal of social function uses the words 'can' and 'could' to give permission or to extend a choice, the words 'can' and 'could' can also express a practical function—someone is able to do something. There are both negative and past forms of the modal of ability.