 As F. P. Ramsey observes in his review of the Tractatus (Ramsey, 1923), the analysis described here actually fails to reveal a logical incompatibility between the two statements in question; for, even granting the correctness of the envisaged reduction of the phenomenology of colour perception to facts about the velocities of particles, the fact that one and the same particle cannot be (wholly) in two places at the same time still looks very much like a synthetic a priori truth. It turns out, however, that Wittgenstein was well aware of this point. He knew that he had not taken the analysis far enough to bring out a logical contradiction, but he was confident that he had taken a step in the right direction. In a Notebooks entry from August 1916 he remarks that: “The fact that a particle cannot be in two places at the same time does look more like a logical impossibility [than the fact that a point cannot be red and green at the same time]. If we ask why, for example, then straight away comes the thought: Well, we should call particles that were in two places [at the same time] different, and this in its turn all seems to follow from the structure of space and particles” (NB, 81; emphasis added). Here Wittgenstein is conjecturing that it will turn out to be a conceptual (hence, for him logical) truth about particles and space (and presumably also time) that particles in two distinct places (at the same time) are distinct. He does not yet possess the requisite analyses to demonstrate this conjecture, but he is optimistic that they will be found. 