The third antinomy

Both sides of the third antinomy assume that whatever happens is caused to happen. The Antithesis says that the only causality is the causality of nature, in which an event is caused by something earlier. The Thesis denies this, in the interests of an alleged causality of freedom, in which the cause does not ante-date the effect. The Thesis-argument is a genuine reductio ad absurdum: it offers no positive doctrine of freedom, but rather presents an alleged difficulty in the Antithesis. I shall now examine this.

The Thesis-argument starts by arguing, quite cogently, that in the causality of nature every cause must be an event or happening. If it were a ‘preceding state’ which ‘had always existed’, its effect ‘also would have always existed, and would not have only just arisen’. This is important, for it implies that if every event is caused through the causality of nature then every event is caused by an earlier event which is caused by … and so on, without beginning. So no causal-explanatory chain can be completed, or, as Kant says, there can be ‘no completeness of the series on the side of the causes’.

What is the difficulty about that? Kant seems poised to raise a problem about infinity, but in fact he does no such thing. The argument concludes thus:

The whole weight falls on the phrase ‘sufficiently determined a priori’, which Kant, typically, does not explain. Here is Kemp Smith's account of what Kant means:

According to this, the Thesis-argument claims that we have not assigned a sufficient cause for an event if we have merely adduced something which in turn needs explanation but is not explained.