Among the more recent attempts to develop more defensible versions of the Regularity View of Causality, J. L. Mackie's (1917–1981) inus-conditions approach stands out. Mackie stressed that effects have, typically, a "plurality of causes" (p. 61). That is, a certain effect can be brought about by a number of distinct clusters of factors. Each cluster is sufficient to bring about the effect, but none of them is necessary. So, he takes the regularities in nature to have a complex form (A&B&C or D&E&F or G&H&I) ↔ E, which should be read as: all (A&B&C or D&E&F or G&H&I) are followed by E, and all E are preceded by (A&B&C or D&E&F or G&H&I). How do we pick out the cause of an event in this setting? Each single factor of A&B&C (e.g., A) is related to the effect E in an important way. It is an insufficient but nonredundant part of an unnecessary but sufficient condition for E. Using the first letters of the italicized words, Mackie has called such a factor an inus condition. Causes, then, are inus conditions. So to say that short circuits cause house fires is to say that the short circuit is an inus condition for house fires. It is an insufficient part because it cannot cause the fire on its own (other conditions such as oxygen, inflammable material, etc. should be present). It is, nonetheless, a nonredundant part because, without it, the rest of the conditions are not sufficient for the fire. It is just a part, and not the whole, of a sufficient condition (which includes oxygen, the presence of inflammable material, etc.), but this whole sufficient condition is not necessary, since some other cluster of conditions, for example, an arsonist with gasoline, can produce the fire.
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