To begin with, there is a conceptual necessity implied in the very concept of cause itself, and in all concepts that have a causal element; and this definitional "must," far from being conventional or arbitrary, reflects the natural necessity of those physical systems which in fact constitute the nature of our universe. The conceptual necessity of the concept of cause can be pointed up in the following way. Assume that we have good reason for saying at to that f, g, (...) h, and i are jointly sufficient to E and hence C of E. What would we say at t1 if f, g, h, and i occurred but not E? We would clearly not say then, or ever, that while ordinarily these conditions are jointly sufficient for E, this time they were not; rather we would say that somehow we were mistaken in thinking that f, g, h, and i at t1 were identical with f, g, h, and i at t0. We might have been mistaken in either of two ways. We might have mis-identified one of the conditions at t1, erroneously thinking, say, that p was an f; or one or more of the conditions might have had its nature altered, losing some capacity or power it once had. In either case, we would withdraw the claim at t1 that C was the cause of E. Since we would withdraw the use of C at t1 and would never admit that f, g, h, and i at any t, if genuine instances of f, g, h, and i, would not produce E, we are clearly using C in such a way that actually producing E is part of its meaning. On the assumption that the conditions are genuinely the same, it follows, so to speak, from the principle of identity that they must produce the same effect. (shrink)