So we must proceed like someone who, having searched for something and not found it where he expected, beats about all the neighbouring fields with no definite view or plan, hoping that sheer good luck will eventually guide him to what he is looking for. We have to leave the direct survey of this question about the nature of the necessary connection that enters into our idea of cause and effect (·returning to it at the start of section 14·), and try instead to find some other questions the answering of which may afford a hint on how to clear up the present difficulty. I shall examine two such questions [the second question is here considerably expanded from Hume’s formulation of it]:
What is our reason for holding it to be necessary that everything whose existence has a beginning also has a cause?
Why do we conclude that causes of kind K1 must necessarily have effects of kind K2, and what is going on when from the occurrence of a K1 we infer that a K2 will occur, and how does it happen that we believe the predictions generated by such inferences?
Before going further, I should remark that although the ideas of cause and effect are derived from impressions of reflection as well as of sensation, for brevity’s sake I usually mention only the latter as the origin of these ideas. Whenever I say anything about impressions of sensation, please take it to be said about impressions of reflection as well. Passions are connected with their objects and with one another just as much as external bodies are connected together. So the same relation of cause and effect that belongs in the external world belongs in the mind as well.