  Schlick’s discussion of the differences between intuition and knowledge laid the groundwork for his treatment of realism. He cautioned, at the outset of his discussion, that the question of realism is not a philosophical problem, but an everyday one. And the view that guides the comings and goings of ordinary life is naïve realism, which assumes that reality consists simply of the objects of sense perception. Of course, the demands of day-to-day affairs seldom require any distinction between the perception of an object and the object perceived, until one encounters an illusion which demands the differentiation of, say, a mirage from a puddle or pond. Only then is a representation first distinguished from its object. It is at this point that the ordinary person realizes that the mirage was real but that the pond or puddle was not.  Thus refined, the naïve criterion of reality is extended beyond the reach of the senses once it is realized that, even when an object is not perceived, its effects provide a sufficient condition of its reality, as when a hunter finds a ravaged animal in the forest and concludes that a predator is in the neighborhood. And it is in precisely this way that naïve realism is naturally extended to include, not just perceptions themselves as well as the objects perceived, but also the causal sources of observed effects. In this way, naïve realism naturally leads to classical causal realism.