Todd Seavey has a good post up about the vacuity of many arguments about who is a “real” libertarian/progressive/liberal/conservative/Scientologist/whatever. And I’ll readily agree that many of these arguments quickly grow petty and pointless. If someone wants to stipulate that by “libertarian” they mean “someone who derives all his political positions from an absolute principle of non-aggression,” I will happily (indeed, eagerly) concede that I’m not one, though I’ll also note that this is apt to result in some confusion among the large numbers of people who employ a less restrictive definition.

Often, however, debates that sound semantic really are substantive. The disagreement is not about what the term means, but about which of two positions is entailed by or more compatible with some set of principles agreed to be at the core of the ideology in question. Here, “You’re not a real X” is best translated as: “You profess to believe X, which is inconsistent with your avowed commitment to Y.”

The nastiest and most pointless arguments of this type probably result when the parties to the dispute have different conceptions of which kind of argument they’re having. Both quickly get frustrated, because one party never realizes that the real disagreement isn’t over what follows from shared premises, but about the premises themselves, while the other recognizes the different premises and can’t understand why they’re getting hung up on some silly tribal argument about who’s got the right to a label.