Abstract: Equitable defences are the front line of controversy over fusion. Because law and equity offer a range of defences that partially overlap and the rationale for matching equitable defences to equitable remedies is at least as obscure as the rationale for separate equitable remedies, conventional wisdom holds that the more one can fuse the equitable defences into the law the better. In this chapter I argue that equity roughly reflects a distinct function - a safety valve that operates at a higher (meta) level over the rest of the law and that responds to problems of high uncertainty and variability. These characteristic problems include opportunism and multipolar conflicts. From a functional point of view, some of the special treatment of equitable defences makes sense, and puzzling patterns in this area receive an explanation and some justification. Even the adaptation of some equitable defences into the law dovetails with a dynamic picture of the equitable function.