This paper outlines a relatively un-noticed fallacy—in the sense of a “mistake in reasoning”—concerning the attribution of motives. It is this: when an agent has multiple motives to perform an action (each of which may be individually sufficient, and each of which she may consciously entertain), it is a mistake to conclude without further evidence that the
worst motive (morally speaking) is the main motive. For obvious reasons, it is hereby
dubbed the “worst motive” fallacy. We outline the fallacy and present experimental results confirming that we are indeed systematically inclined to commit it.