I am asking when it is true to report, in the past tense, that one event has caused another to occur. My question derives from a much-discussed puzzle in action theory, about how to individuate what we do in those familiar circumstances where we perform action A by doing B. For an example of B, suppose that I reach out my arm. In so doing, I slam a door that was in contact with my arm-thus carrying out action A. The individuation riddle will be: How many separate deeds have I performed? As many as when I simultaneously turn my head and thrust out my arm? This inquiry may sound trifling; yet it could set us on the right track toward an understanding of some 'deeper' notions-for instance, what it is to do one thing as a means of doing another; the relationship of acts to their consequences; and the mysterious but paradigmatic action of causing something to happen. Eventually we will see how debates over individuation lead to my title question. But first I should furnish minimal stage setting. By reference to our example, one group of philosophers, best represented by Jaegwon Kim (i966; with Brandt, i967) and Alvin Goldman (I970, I971), would individuate A and B as distinct performances. Accordingly, I call such theorists 'multipliers'. Their reason for sundering A from B is, ultimately, that A has properties which B lacks, and conversely. The other leading account is suggested by G. E. M. Anscombe (i957, pp. 44 f.) and elaborated by Donald Davidson (i963, pp. 686 f.; i969a, b; I97i). These writers hold that A is nothing over and above B; hence I dub them 'reductive unifiers'. On principle, I share Davidson's reluctance 'to suppose that when I close the door by moving my hand I perform two numerically distinct actions'; and like Davidson, I am inclined to 'oppose any view that implies that if I do A by doing B then my doing A and my doing B must be numerically distinct' 097I, p. 20). Why not let individual acts proliferate in this manner? Among many rationales I have heard, the simplest one for being ontologically stingy is that I have no need, either while or after I stretch out my arm, to undertake some 'additional' act of door-slamming. The door is going to bang shut anyway -not by itself, to be sure, but as a result of my arm-stretching (Davidson, I97I, p. 2I; see Thomson, I97I, pp. II5, II9, I2I, I27; and for further reasons, Davidson, I969b, pp. 2I7 f., 222 f.). The controversy is worth exploring because each side has tough arguments, and also because each takes it for granted that you must be either a multiplier or a red active unifier. For Davidson, the sole alternative