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A Puzzle About Causation

by Stephen Mumford

Imagine a game show between two teams of four players. When a member of the team knows an answer they press a button and the team light comes on. Each team member has their own button and just one of them has to press for the light to come on. Two, three or four team members may know the answer and press their buttons. Who caused the light to light-up? Surely the one who pressed first, even if their teammate( s) would have lit the light had they failed to do so. But what if all four pressed simultaneously? None can claim to have caused the light to go on because their individual effort was quite superfluous.

Philosophers have found causation particularly perplexing. The traditional problem has come from Hume; is there anything more to causation than a constant conjunction of events, and if not, then how do we exclude ‘accidental conjunctions’? If every time I sneeze, you cough, does this mean that my sneezing causes your coughing?

I am drawing attention to a problem which receives less consideration. Must there be one (and only one) cause of each effect or can some effects have two or more causes? Can we allow that two separate causes are sufficient for the same event such that the event would have occurred had one of the causes been absent? This question is significant for the philosophy of mind where we have both mental and physical events as rival causes of a human action. It is also significant for theories about dispositions, when we consider whether a dispositional property caused its manifestations or a molecular structure did. In such cases we have two events or properties, apparently with equal claim to causal efficacy. An explanation of these problems would be somewhat involved however and we would do best to consider the problem at its origin – in the concept of causation.

I can explain the force of the problem further by posing it as a dilemma. The dilemma arises quite naturally out of the concept of cause, which produces two evidently conflicting intuitions.

1. The cause of an effect is unique (the principle of uniqueness).

If the throwing of the brick was the cause of the window breaking, then nothing else caused it. If my rude behaviour was the cause of your anger, then nothing else was the cause of your anger. In general, the concept of cause seems to exclude anything but a singular cause of any effect. It may be objected that some effects clearly have more than one cause; the tree fell because its roots were weak and the wind blew. This is not the type of case I am getting at however. Here we cannot say that the cause of the tree falling was its weak roots (or that it was the blowing of the wind) because one of the factors alone would not have resulted in the fallen tree. The cause is the sum of both factors; that the wind blew and that the roots were weak. These two factors are jointly sufficient for the production of their effect though neither would have been sufficient on its own.

We can say therefore, that each effect has a single cause, even if that cause is a complex of more than one constituent.

Though the uniqueness of causation seems to gain our consent, it seems also that we cannot deny the occurrence of ‘overdetermination’ – our second intuition.

2. Some effects are overdetermined.

We say that an effect has been overdetermined when it has two distinct causes, each of which alone would have been sufficient for the effect. For example, both the instructor and the learner in a dual control car may press their brake pedals at the same time and the car will stop. As long as one of them brakes, the car stops, but in this case both of them press their brake pedal. What causes the car to halt? Is it the instructor braking or is it the learner braking? This is not a case of joint sufficiency, for neither person braking was necessary for the stopping of the car. If the instructor had trusted their pupil and not gone for their brake the car would still have stopped because of the pupil pressing their brake. Alternatively, if the instructor had braked but the pupil had not, again the result would have been the same. We can say, to sum up the situation, that for the car to stop it is necessary that at least one of the instructor or the learner press their brake pedal, for each brake-pressing is sufficient for a car-stopping. However, it is not necessary that both press their brake pedal as long as one of them does; either way, the effect is the same.

If there are genuine cases of overdetermination then the uniqueness principle would appear to be false.

Before considering the puzzle, let us first discount some apparent cases of overdetermination which are not quite in the same category.

It may be said that as long as the instructor is doing their job it is never necessary, for the car to stop, for the learner to brake. A good instructor will always stop the car at the right time if the learner fails to do so. We could conclude that the car will always stop when needed whether or not the learner brakes. A similar case to this would be where two of us desire that a particular window be broken. It could be said that your brick going through the window was not necessary to its breaking because, had it missed, mine would have smashed the window a short while later.

A different type of case is where the dual control car would have stopped had either the learner or the instructor braked but if they both brake simultaneously, through their joint efforts, the car stops much sharper and in a shorter distance. Similarly, an ice-lolly will melt if left in the sun or if left near a fire, but if exposed to both it melts in double time.

I do not class these as genuine cases of overdetermination because the caused event is different in the two possible situations. In the first group of cases, had the one possible cause failed to occur, the second would have ensured the production of the effect but at a later time. Although the same type of effect would have been brought about it would not have been the very same effect, for it would have occurred at a different time. With the second set of cases, where both causal factors occur, the effect occurs in a different manner; stronger, more intense or quicker. Again we say that it is not exactly the same event that is produced when both causal factors are involved; this is really another case of joint sufficiency where an effect is caused by a complex of factors, each necessary for the production of that effect.

Genuine cases of overdetermination are those where an effect has two or more simultaneous causes, each of which alone would have been sufficient for the production of the effect, and the effect would have been the same had either, but not all, been absent.

Now what are we to say about such cases? Are we to say that they render the principle of uniqueness in causation false? Could we deny that any such cases of overdetermination actually exist? Are the examples misleading? We could offer more detailed descriptions of the examples and try to explain away the appearance of overdetermination, but no number of such explanations would rule out overdetermination a priori. It looks bad for the principle of uniqueness in causation.

But wait. Wouldn’t it also be counterintuitive to abandon the principle? Effects seem to demand a single cause and in their demand for ‘singularity’ they are not alone. Consider the similar case; if I painted the picture then no-one else did. If others painted it with me then we painted the picture and I cannot be said to be the painter of the picture but only a painter of part of it. This is just like causation; if I caused the car to stop, then no-one else did. If someone else stopped the car, then I didn’t stop the car.

Are our ordinary intuitions enough in this case or have they lead us to an irresolvable contradiction? Should we abandon reliance on the ordinary concept of causation and seek a new revised and improved version which is contradiction free, or have we merely made a mistake in unpacking the concept of causation?

The puzzle arising out of causation is indicative of a much wider debate; should we be defenders or revisionists of ordinary usage? Philosophers, when they ask ‘what is…?’ questions, are frequently attempting the analysis of common concepts and trying to explicate such meanings as faithfully as possible. A long line of revisionists – Leibniz, Frege, Russell and Carnap – would have said that the job of the philosopher is to eliminate the confusion and imprecision of our everyday language. We must decide where the error lies. Do we make philosophical errors because we fail to understand ordinary language correctly, or because we persist in using it?

Stephen Mumford is a postgraduate philosopher at the University of Leeds