Ifs and Cans
IF someone were to ask what idea is expressed by the verb ‘can’ in all its moods and tenses, he might be told that it expressed power, potency or potentiality, capacity, capability or ability, contingency or possibility-all or some of these. But this answer, though true enough, is unenlightening, and unenlightening just because it is so obviously true. If there are puzzles about ‘can’ there will be puzzles about these. Human actions, the things people actually do, are, we feel, ground-floor members of the world; their abilities are not. Philosophers have often felt that particular statements, expressed by sentences in the indicative mood with names of entities as subjects, are somehow paramount. We use the indicative mood to say flatly that something is or was or will be the case. Hypothetical and universal statements, by contrast, are suspect. This feeling has led some philosophers (for example some logicians who have been incautious about the relation between the logical constants of a language and those of a calculus) sadly astray. It is certainly wrong to say flatly that ‘all mules are sterile’ means the same as ‘if anything is a mule, it is sterile’ or ‘nothing is both a mule and non-sterile’; but the idea that it is not sufficiently categorical to get in on the ground floor but requires to show its connexions with true-blue categoricals about this and that mule before it can be
admitted is not wholly erroneous. Likewise statements about the next mule are not wholly irreproachable, and the drive to analyse universal statements into hypotheticals and then treat these hypothetical as truth-functional sets of particular categoricals is not wholly to be resisted.