What Independence Is

Eighty years ago, in a short essay entitled “What Is Independence?,” Richard Robinson (1902-1996) made two errors that, to my knowledge, remain uncorrected. The errors are (1) claiming that entailment entails consistency (it does not) and (2) misstating the relation of subcontrariness. To make good on my claim that these are errors, I present and explain, in a more systematic way than Robinson does, nine distinct logical relations, one of which is independence. There are independent reasons for making these relations—as well as their relations to one another—better known to philosophers.