 Once the problem is put like that, however, the panpsychism problem looks similar to a problem that arises in general whenever one one tries to understand or define a concept in terms of paradigmatic objects which fall under it, viz., that these definitions have certain sort of empirical presuppositions that might turn out to be false. Suppose one tried to define the concept red in terms of similarity to paradigmatic red things, such as blood. Pursuing this strategy commits one to the idea that the belief that blood is red is a piece of common knowledge shared among all those who are competent with the term. But that seems wrong — someone who thought that blood was green would be mistaken about blood but not about red. Now this problem is a difficult problem, however — and this is the crucial point for our purposes — the problem is also a quite general problem; it arises because of the paradigm style of definition. So to that extent, the concept of the physical does not seem to be any worse off than the concept of red, the panpsychism problem notwithstanding. (For discussion of the general strategy see Lewis 1997)