Abstract

Sam signaled a turn by extending his arm out the window. Difficulties in explaining the asymmetry of the by-relation in such examples by reference to acceptable and unacceptable counterfactual conditionals are explored by Hugh McCann in "The Trouble with Level-Generation" ("Mind", October 1982). I refine and defend the following alternative account of one-way dependence of y on x: not only is x necessary for y, but something else, independent from x, is also necessary for y; but there is nothing independent from y such that it and y are each necessary for x.