thus determined by a previous event, and so on indefinitely. This means there can be no first beginning, and thus the series of causes cannot be completed. According to the law of Nature, though, nothing happens without a cause sufficiently determined a priori, and this law cannot be fulfilled if the causality of every cause is itself an effect of an antecedent cause. This means there must be an absolutely spontaneous causality which originates a series of phenomena that then proceeds according to natural causes. The antithesis is proven by noting that spontaneous, free causation presupposes a state of the cause which stands in no causal relation, or that stands as effect, to the preceding state. This presupposition, though, is contrary to the natural causal law and would render impossible the unity of experience. Therefore, freedom is not to be found in experience and is a mere fiction of thought (Copleston 289-290).
John Greenwood notes the importance of the third antimony in raising issues about the relationship between our beliefs about human freedom or agency and the universality of causal explanation, said to be a perennial philosophical problem:
Most philosophical and psychological accounts of the relation between agency explanations of human action in terms of agent reasons, and causal explanations in terms of empirical conditions, propose to resolve the issue either by treating agency explanations as non-causal or by treating agency explanations as ordinary causal explanations. . . (Greenwood 43).
Greenwood sees Kant's discussion of the problem as a particularly clear statement of the issue, though it is restricted to the question of the relation between the presuppositions of explanations of moral actions and ordinary causal explanations. The problem arises, says Greenwood, because of the apparent inconsistency of the presuppositions of morality and scientific causal explanation:
Kant is concerned specif...