David Hume called causation the “cement of the universe”, and he was convinced that psychologically and in our practices, we can’t do without it.

Yet he was famously sceptical of any attempt to analyze causation in terms of necessary connections. For him, causation can only be defined in terms of a constant conjunction in space and time, and that is, I would add, no causation at all, but correlation. For every two events that seem causally connected can also, and without loss of the phenomenon, be described as just the first event, followed by the second. It’s really “just one damn thing after another”. It seems to me we still cannot, will not and need not make sense of the notion of causation (virtually no progress has been made since Hume's time).

There seems no need for another sort connection besides the spatio-temporal one, nor do we perceive any. In philosophy, a Hume world is a possible world defined in this way. All the phenomena are the same, but no necessary connections hold between the supposed relata. Maybe one should best imagine such a world as a game of life-world, but without a fundamental level governed by laws and forces; or as a movie, made of frames that are not intrinsically connected to each other. So, however strong the psychological forces that drive humans to accept further mysterious connections: Shouldn't we just stop worrying and accept living in a Hume world? Or are there actual arguments in favour of "real" causation?

It is a commonplace that correlation does not imply causality, however eyebrow-wagglingly suggestive it may be of causal hypotheses. It is less commonly noted that causality does not imply correlation either. It is quite possible for two variables to have zero correlation, and yet for one of them to be completely determined by the other.