 It’s a very natural suggestion that if the negative claim that a isn’t F is true it’s made true by the existence of something positive that’s incompatible with a’s being F (Demos 1917). For example, the truth-maker for the claim that kingfishers aren’t yellow is the fact that they’re blue because their being blue is incompatible with their being yellow. But what makes it true that these colours are incompatible? The notion of incompatibility appears itself to be negative—a relation that obtains between two states when it’s not possible for them to obtain together. So this proposal threatens to become regressive: we’ll need to find another positive truth-maker for the further negative claim that yellow and blue are incompatible, something whose obtaining is incompatible with the state of yellow and blue’s being compatible, and so on (Russell 1918–9: 213–5, 1919: 287–9; Taylor 1952: 438–40; Hochberg 1969: 330–1; Grossman 1992: 130–1; Molnar 2000: 74–5; Simons 2008). There’s another worry: it’s not obvious that there are enough positive states out there to underwrite all the negative truths there are. Even though it may be true that this liquid is odourless this needn’t be because there’s something further about it that excludes its being odorous (Taylor 1952: 447; Mulligan, Simons, &amp; Smith 1984: 314; Molnar 2000: 75; Armstrong 2004: 62–3; Dodd 2007: 387).