Humean causation

One of the most important contributions of David Hume (1711-1776) to philosophy is his view on causation. In several respects it is controversial and much has been said about it. Despite all criticisms it contains some essential elements of the idea of causation that you find back in almost any discussion about it, if not that they are present in the background. Therefore it’s worth giving here Hume’s view. I’ll base myself mainly on his essay “Of the Idea of Necessary Connexion”. (first published in 1748) A deeper explanation can be found in his Enquiry concerning Human Understanding (1748).
However, let me start with the lemma on Hume in the Stanford Encyclopedia of Philosophy. In section 2.2 it says that “Hume takes there to be three components to our idea of causation: first, spatial contiguity, second, priority in time of cause before effect, and most importantly, the necessary connection between cause and effect.” However, this summary of Hume’s idea of causation omits what is, to my mind, Hume’s most important and also most essential aspect of causation: That “all our ideas are nothing but copies of our impressions”, and that consequently the idea of causation, so of cause and effect, exists only in the mind: We don’t know anything about what happens in reality: “[W]e are never able, in a single instance, to discover any power or necessary connexion; any quality, which binds the effect to the cause, and renders the one an infallible consequence of the other. We only find, that the one does actually, in fact, follow the other. The impulse of one billiard-ball is attended with motion in the second. … [T]he power or force, which actuates the whole machine, is entirely concealed from us…” We can never know anything about the power that connects a cause and an effect. If we think that there is such a connection, it’s only based on our experience of how one event constantly follows another, but we cannot know what a cause and effect “binds … together and makes them inseparable.” We don’t understand the connection but we only see a conjunction of objects.
Until now we discussed only connections between individual events. In fact, experiencing a connection between individual cases is not enough to speak of a causal connection, how certain and accurate this connection may seem to us. We can only suppose a causal relationship to be present if it always exists, i.e. if “one particular species of event has always, in all instances, been conjoined with another.” There must be a constant conjunction of two events. However, even then, not much changes, “except only, that after a repetition of similar instances, the mind is carried by habit, upon the appearance of one event, to expect its usual attendant, and to believe, that it will exist.” Also a constant conjunction is nothing but a feeling, an experience, a “customary transition of the imagination from one object to its usual attendant”, and it “is the sentiment or impression, from which we form the idea of power or necessary connexion. Nothing farther is in the case.” In short (my words), a causal connection exists only in the mind and says nothing about what really happens. It makes foretelling the existence of one from the appearance of the other easy, indeed. However, “[w]hen we say … that one object is connected with another, we mean only, that they have acquired a connexion in our thought, and give rise to this inference, by which they become proofs of each other’s existence.”
Therefore, so Hume, “we may define a cause to be an object, followed by another, and where all the objects, similar to the first, are followed by objects similar to the second. Or in other words, where, if the first object had not been, the second never had existed. The appearance of a cause always conveys the mind, by a customary transition, to the idea of the effect. Of this also we have experience. We may, therefore, suitably to this experience, form another definition of cause; and call it, an object followed by another, and whose appearance always conveys the thought to that other.” However, we have no idea what such a connection involves.
In his Enquiry concerning Human Understanding Hume mentions contiguity in time and space as a requirement for a connection of ideas. This should exclude the idea of remote causation. This gives us the three elements of causation as contiguity, priority in time of cause before effect, and necessary connection. However, so Hume, “[e]very idea is copied from some preceding impression or sentiment; and where we cannot find any impression, we may be certain that there is no idea.” When the vase falls to the ground just at the moment that the crow caws, it is only in our mind that the latter causes the former (or the other way round).