You let go of a glass. It proceeds to smash on the floor. What causes were involved? Your decision to release your grip? Some ‘pushing and pulling’ in the world, natural laws governing your decisions and the glass’ smashing? Something else?

David Hume called it a habit of the mind. Bertrand Russell said it is ‘the relic of a bygone age’. David Chalmers claimed our discussion of it is ‘over and above’ what happens in the physical world. We are, of course, talking about causation. What even is it? For many philosophers it is nothing at all.

Perhaps causation is simply what regularly co-occurs (e.g. drop → smash), the increase of probability, or the transfer of information. Alternatively, it’s born in us as animal agents who mentally manipulate their physical surroundings in decision-making.

It’s very easy to ‘overdetermine’ an effect with too many causes. For example, did the Big Bang cause you to read this post? Did you cause your own death by eating a dinner laced with poison by your ex?

With one concept we want to capture the small (e.g. atomic decay), the large (e.g. thermonuclear explosions hurling matter across cities), and the non-physical (e.g. economic crises). Then there are absences (e.g. forgetting to water a plant, killing it). Language implies causal roles (e.g. ‘killing’) but we lack precision.

A popular theory emerged in recent times, inspired by the views of David Lewis, whereby causation is explained as ‘counterfactual conditionals’: if X had not occurred, Y would not have occurred.

Consider two people, Salt and Pepa, who together plan to shoot and kill a third person, Chips. They pull their triggers simultaneously. Only one wound is fatal.

According to Lewis, since we don’t know whose bullet fatally wounds Chips in the general case (‘at all possible worlds’), Chips’ death only quasi-depends on the shots. Why? For there is no counterfactual conditional: if Salt’s bullet isn’t fatal, Pepa’s is. And, by a technicality, there is no overdetermination.

In actuality the coroner determines that it was Salt’s bullet that caused Chips’ death. Who will the court prosecute?