Counterfactuals is David Lewis' forceful presentation of and sustained argument for a particular view about propositions which express contrary to fact conditionals, including his famous defense of realism about possible worlds and his theory of laws of nature.

Many philosophers have believed that the laws of nature differ from the accidental truths in their invariance under counterfactual perturbations. Roughly speaking, the laws would still have held had q been the case, for any q that is consistent with the laws. (Trivially, no accident would still have held under every such counterfactual supposition.) The main problem with this slogan (even if it is true) is that it uses the laws themselves to delimit qs range. I present a means of (...) distinguishing the laws (and their logical consequences) from the accidents, in terms of their range of invariance under counterfactual antecedents, that does not appeal to physical modalities (or any cognate notion) in delimiting the relevant range of counterfactual perturbations. I then argue that this approach explicates the sense in which the laws possess a kind of necessity. (shrink)

There is, no doubt, a temptation to treat preventions, such as ‘the father’s grabbing the child prevented the accident’, and cases of ‘causation’ by omission, such as ‘the father’s inattention was the cause of the child’s accident’, as cases of genuine causation. I think they are not, and in this paper I defend a theory of what they are. More specifically, the counterfactual theory defended here is that a claim about prevention or ‘causation’ by omission should be understood not as (...) being directly about actual genuine causation but primarily as a counterfactual claim about genuine causation.1 The relation between actual causation and the mere possibility of causation allows my theory to explain both the difference and the similarity between the two notions (causation and prevention/omission). Further, the difference explains certain intuitions we have and the similarity justifies and explains the fact that for practical purposes we usually treat preventions and omissions as if they were genuine causation. Finally, the fact that this counterfactual theory of prevention and omission takes causation as primitive suggests that it is consistent with any theory of causation. This allows us to construct two arguments against what I will call genuinism, the view that cases of prevention and ‘causation’ by omission really are cases of genuine causation. In section II I show that genuinism does not account for the so-called intuition of difference. In section III I outline a number of problems that various theories of causation have with preventions and ‘causation’ by omission. These problems are ipso facto problems for genuinism, whereas I show in section V how the counterfactual theory solves those problems. Further, I answer a genuinist argument based on another type of intuition—the genuinist intuition—by showing why we have that intuition and how it should be handled (section VI). (shrink)

It seems to be generally accepted that (a) counterfactual conditionals are to be analysed in terms of possible worlds and inter-world relations of similarity and (b) causation is conceptually prior to counterfactuals. I argue here that both (a) and (b) are false. The argument against (a) is not a general metaphysical or epistemological one but simply that, structurally speaking, possible worlds theories are wrong: this is revealed when we try to extend them to cover the case of probabilistic counterfactuals. Indeed (...) a type of counterfactual probability exists which cannot be expressed in possible worlds terms at all. The argument against (b) emerges when we look at the form of an adequate account of both probabilistic and non-probabilistic counterfactuals. I do this by sketching and defending an approach to counterfactuals that, first, invoke a generalized notion of cause as primitive and, secondly, is algorithmic in form: counterfactuals are evaluated algorithmically in terms of other counterfactuals, without vicious circularity. Structures like possible worlds do not play a role either in general truth-conditions or in evaluation. They are simply the wrong sorts of structures. (shrink)

This volume is devoted to Lewis's work in metaphysics and epistemology. Topics covered include properties, ontology, possibility, truthmaking, probability, the mind-body problem, vision, belief, and knowledge. The purpose of this collection, and the volumes that precede and follow it, is to disseminate more widely the work of an eminent and influential contemporary philosopher. The volume will serve as a useful work of reference for teachers and students of philosophy.