What can be true or can be done varies with the meaning of "can." As far as philosophy is concerned, the important senses of this word ("could," past indicative) fall into five major groups. For convenience these groups, most of which are distinguished in Webster's Third New International Dictionary, may be singled out as the "can" of ability, of right, of inclination or probability, of opportunity, and of possibility.

"Can" of Ability

The "can" of ability has at least three subsenses: (1) to have the skill—"He can speak five languages or paint lifelike portraits"; (2) to have the requisite mental or physical power—"He can solve difficult problems, invent remarkable machines, or foretell the future" or "He can swim a mile or do one hundred push-ups"; (3) to have the requisite strength of character—"He can resist anything but pleasure, pass up a free drink, or bear criticism of his...