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Tractatus Logico-Philosophicus by Ludwig Wittgenstein + comments  by Maarten Maartensz   



6.3751 For example, the simultaneous presence of two colours at the same place in the visual field is impossible, in fact logically impossible, since it is ruled out by the logical structure of colour. Let us think how this contradiction appears in physics: more or less as follows--a particle cannot have two velocities at the same time; that is to say, it cannot be in two places at the same time; that is to say, particles that are in different places at the same time cannot be identical. (It is clear that the logical product of two elementary propositions can neither be a tautology nor a contradiction. The statement that a point in the visual field has two different colours at the same time is a contradiction.)

All of this is false, for a very simple reason: Light mixes. Take one filter and produce blue light from one lamp and another to produce yellow light from another lamp, and project the two beams on top of another on a white plane, and behold green.