PHILOS 132 Final: Summary of Kripke's argument against identity thesis
Document Summary
Consider the following identity statement: the morning star is the evening star . To understand how kripke claims that this is necessary, we need to understand both what necessity is and what rigid designators are. Leibniz defined necessity as truth in all possible worlds (lec 6). So when we say that the morning star is the evening star, we are saying that there does not exist a possible world where the morning star is not the evening star. A rigid designator is a name (329) - it names an object. So diogenes names (that is, it picks out) the particular object, the psychophysiological entity (perhaps specified by his genetic makeup), diogenes. In another possible world, facts about diogenes could have been different. He could have been a sculptor, instead of founder of cynicism. But when we name (or rigidly designate) a thing as diogenes, we are tagging that particular psychophysiological entity.
