Lewis (David)
Source: Lewis - Philosophical Papers Volume II, Part 6: Causation, Chapter 21
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Author’s Introduction

  1. Hume defined causation1 twice over. He wrote "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."
  2. Descendants of Hume's first definition still dominate the philosophy of causation2: a causal succession is supposed to be a succession that instantiates a regularity. To be sure, there have been improvements. Nowadays we try to distinguish the regularities that count – the "causal laws" – from mere accidental regularities of succession. We subsume causes and effects under regularities by means of descriptions they satisfy, not by overall similarity. And we allow a cause to be only one indispensable part, not the whole, of the total situation that is followed by the effect in accordance with a law. In present-day regularity analyses, a cause is defined (roughly) as any member of any minimal set of actual conditions that are jointly sufficient, given the laws, for the existence of the effect.
  3. More precisely, …
  4. Much needs doing, and much has been done, to turn definitions like this one into defensible analyses. Many problems have been overcome. Others remain: in particular, regularity analyses tend to confuse causation3 itself with various other causal relations. If c belongs to a minimal set of conditions jointly sufficient for e, given the laws, then c may well be a genuine cause of e. But c might rather be an effect of e: one which could not, given the laws and some of the actual circumstances, have occurred otherwise than by being caused by e. Or c might be an epiphenomenon of the causal history of e: a more or less inefficacious effect of some genuine cause of e. Or c might be a preempted potential cause of e: something that did not cause e, but that would have done so in the absence of whatever really did cause e.
  5. It remains to be seen whether any regularity analysis can succeed in distinguishing genuine causes from effects, epiphenomena, and pre-empted potential causes – and whether it can succeed without falling victim to worse problems, without piling on the epicycles, and without departing from the fundamental idea that causation4 is instantiation of regularities. I have no proof that regularity analyses are beyond repair, nor any space to review the repairs that have been tried. Suffice it to say that the prospects look dark. I think it is time to give up and try something else.
  6. A promising alternative is not far to seek. Hume's "other words" – that if the cause had not been, the effect never had existed – are no mere restatement of his first definition. They propose something altogether different: a counterfactual analysis of causation5.
  7. The proposal has not been well received. True, we do know that causation6 has something or other to do with counterfactuals. We think of a cause as something that makes a difference, and the difference it makes must be a difference from what would have happened without it. Had it been absent, its effects – some of them, at least, and usually all – would have been absent as well. Yet it is one thing to mention these platitudes now and again, and another thing to rest an analysis on them. That has not seemed worthwhile. We have learned all too well that counterfactuals are ill understood, wherefore it did not seem that much understanding could be gained by using them to analyze causation7 or anything else. Pending a better understanding of counterfactuals, moreover, we had no way to fight seeming counterexamples to a counterfactual analysis.
  8. But counterfactuals need not remain ill understood, I claim, unless we cling to false preconceptions about what it would be like to understand them. Must an adequate understanding make no reference to unactualized possibilities? Must it assign sharply determinate truth conditions? Must it connect counterfactuals rigidly to covering laws? Then none will be forthcoming. So much the worse for those as statements about possible alternatives to the actual situation, somewhat vaguely specified, in which the actual laws may or may not remain intact? There are now several such treatments of counterfactuals, differing only in details. If they are right, then sound foundations have been laid for analyses that use counterfactuals.
  9. In this paper, I shall state a counterfactual analysis, not very different from Hume's second definition, of some sorts of causation8. Then I shall try to show how this analysis works to distinguish genuine causes from effects, epiphenomena, and preempted potential causes.


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