English - Advanced Grammar - Modals and modal verbs - Modal Nuances
6 steps: (1) Modals NEVER change form (no -s, -ed, -ing): 'She can swim' NOT 'She cans swim.' Always followed by BASE verb: 'must go' NOT 'must to go' or 'must going.' (2) Certainty scale: WILL (100%) > MUST (95%) > SHOULD (80%) > MAY (50%) > MIGHT/COULD (30%). 'She must be tired' = I'm almost certa