The following beliefs can be ascribed to Hume on the basis of his writings:
(1) There is no more to our idea of cause and effect than constant conjunction and a resulting habit of mind.
(2) There is more to it than that, namely the interaction of bodies.
(3) Behind the constant conjunctions, including the interactions of bodies, there are ‘secret’ causes, not knowable by man.
(4) The principle of causality (nothing happens without a cause) is true.
(5) Our belief in the principle arises from experience.
(6) There is no justification for believing in the principle.
It is obvious that there are inconsistencies between these beliefs. (1) is contradicted by (2) and (3), and (3) appears to contradict (2). (4) and (5) are consistent, but (4) cannot be asserted consistently together with (6). There is apparently a contradiction between (5) and (6), although (as often happens when discussing Hume) the question arises whether ‘arising from experience’ is to be regarded as a justification. In the next section I shall offer support for ascribing these beliefs to Hume and in sections III-V I shall try to say why Hume wanted to hold all of them in one way or another and how they fit together in the context of his philosophy. What I shall say will I be broadly in line with Passmore's views about the diversity of Hume's intentions and Kemp Smith's thesis about Hume's primary interest in ethics.