Semantic Slippery Slope Fallacy
The Semantic Slippery Slope is a fallacy that occurs when someone argues that because there is no clear line between two concepts or because they "only" differ in degree, therefore either they are the same thing or neither exists at all.
This fallacy is somewhat of an inversion of the False Dichotomy, in which someone ignores any grey area and posits that only two contrasts exist. The Semantic Slippery Slope emphasizes any grey area and disregards clear differences. In short, saying the concept is too vague for any real decision to be made. The Semantic Slippery Slope Fallacy is also related to the regular Slippery Slope Fallacy insofar as committing the former will often cause the latter by inferring that one thing will inevitably cause the second thing, or that they're the same thing altogether.
- This is also known as "Loki's Wager". In Norse Mythology, Loki wagered that two Dwarven blacksmiths could not make a particular weapon and offered his head as collateral. When the Dwarves succeeded, they demanded Loki's head, but he made their claim irrelevant by stating that they had won only his head, and that since there is no clear line where the head ends and the neck begins, they could not take the former without also taking the latter. The term "Loki's Wager" has become used as an alternative name for this very fallacy.