 The third and last of these unified notions of causation is physicalist in its ambitions. Some theorists have thought that we can say more about the nature of the causal relation than that it is scalar and that a substantial amount of it is required for responsibility. On this third view, the nature of causation is to be found in the mechanistic concepts of physics: matter in motion, energy, force (Beale 1895, 1920; Epstein 1973). This test is similar to the substantial factor view in its conceiving the causal relation to be scalar but differs in its reductionist ambitions: causation is not a primitive but can be reduced to some kind of physical process.