Loki is the trickster god of Norse mythology, pictured here in an 18th-century Icelandic manuscript illustration. At one point in the Prose Edda, a 12th century compilation of Norse mythology by the Icelandic poet Snorri Sturluson, Loki wagers his own head in a bet with the dwarf Brokkr. Loki loses the bet but doesn't lose his head because he insists that his neck was never included in the bargain. Since Loki and Brokkr cannot reach a consensus as to where Loki's neck ends and his head begins, the dispute remains forever unresolved, and Loki retains his head. It's pretty much the same principle as the "pound of flesh but not a drop of blood" in The Merchant of Venice.
In the theory of argumentation, the fallacy of Loki's Wager is "the unreasonable insistence that a concept cannot be defined, and therefore cannot be discussed." It tends to be used, whether intentionally or not, as a stalling or diversionary tactic which ensures that the real issue need never be debated because there can be no consensus on the terms of debate. In my opinion, it lies somewhere between a red herring and an equivocation on the continuum of logical errors. It is also one of the most commonly seen fallacies on the internet, especially in political debate, and sometimes devolves into name calling when the term that is being negotiated is one of opprobrium, like "terrorist," "murderer," or "liar." Usually this happens when such terms are broadened rather than narrowed so that the term of opprobrium threatens to wash over the opposing party in the debate. For example, most people can agree that they are against "murder" when it is defined as "the unlawful taking of a human life with malice aforethought," but when one party of the debate insists on defining "murder" as any form of killing and then calls for the killing of animals for food to be condemned as murder, the ethics of a commitment to vegetarianism can never be argued because the debate will remain forever in the realm of contested definitions -- obviously so, since meat-eaters cannot agree to call themselves murderers. A brief survey of the blogosphere will reveal Loki's Wager in active use for practically every contested issue in the body politic, from abortion to Iraq to globalization to fast food to health insurance to cigarette smoking.
This is not to say that arguments about word boundaries are invalid, but that an insistence on boundaries that can't be agreed upon is a barrier to further debate on issues that require consensus if those terms are to be used. The solution is to set aside the semantic debate and use mutually acceptable terminology to continue the discussion. This can't be done when the contested term forms the philosophical basis or warrant of the debate. It is virtually impossible to argue the abortion issue without a consensus on the word "person," for instance, and since the definition of the word "person" is the basis of the disagreement it is impossible to set it aside.
