So far, what we have is an argument for the thesis that reasoning from causes to effects is brought about by the associative mechanism of causation, and an account of how that mechanism operates. As we have already seen, in the case where the input to the mechanism is a present impression of event c plus the memory of past constant conjunction of Cs and Es, that mechanism does not simply deliver the belief in e; in addition, we come to think of c as the cause and e as the effect. But what we don’t have is an account of the origin of the idea of necessary connection. All we know is that the associative mechanism somehow enables us to think of causes and effects as causes and effects. And so Hume turns his attention – in Book I, Part III, §XIV of the Treatise and §7 of the Enquiry, both entitled ‘Of the idea of necessary connexion’ – to tracing the impressionsource of the idea of necessary connection. These sections are the focus of this chapter.