Richard is interested in things like billiard ball collisions, which was the sort of case Hume began with, and uses as an example in his Abstract and in EHU. But he generalised his account of our acquaintance with causation as merely experience of regular sequence to the psychological cases, such as Jim's case of being startled by a noise, saying "The uniting principles among our internal perceptions[such as hearing a noise then being startled] is as unintelligible as that among external objects , and is not know to us any other way than by experience." (T 169) Yet when in his Appendix he takes this claim seriously, and sees all his own perceptions as having mere correlations uniting them, not really efficient causation, he feels something has gone wrong, and he has no adequate account of his own mind, and what unites his own perceptions. His initial analysis of the causal relation had found it to consist in temporal sequence, spatial contiguity (where applicable) and necessity, so he may have gone wrong at the start, as its unclear that we do regard causes as necessitating their effects. So he was launched on his quest to track down the origin of the idea of causal necessity, and failed ot check if the idea of "efficacy" really was the same as that. As Anscombe pointed out, we do think we know that the knife pressed onto the cheese cuts it, the first time as much as any subsequent time. Hume did allow that sometimes we are sure of a causal connection after one case, so generalize from that, but thought this was because of our familiarity of hundreds of similar but not quite the same causes.But I think his main error was in taking necessity to be part of what we take causation to be. He may also be wrong in thinking our knowledge of how our own nature works is the same as our knowledge of how the rest of nature works, so he treats his own perceptions as if they were as separate as billiard balls.it possible that Locke was right that our idea of power does originate in our own exercised powers, not just of our wills but our muscles, in pushing, pressing etc. When Hume argues against Locke, it is the will as efficacious cause he dismisses. Of course for Berkely too the will's moves are not passive ideas, and we have notions of them, not ideas. Hume is so set against the Locke-Berkeley priviliging of the human will that he fails to ask if other aspects of our psycholigy might not reveal efficacious causation to us, without displaying necessity. This is just a note on Hume's approach, and does not advance your main concerns,  Annette Baier.