Suppose a pigeon pecks at crimson tiles. Is the pecking caused by the specific shade, crimson, or the more generic colour, red? The natural answer is that it depends. If the pigeon pecks only at crimson tiles, and not at other shades of red, then it is the crimsonness that is causing the pecking; but if the pigeon pecks at any shade of red, it is the redness. Examples like these have led a number of writers to require that causes be proportional to their effects (Yablo 1992; Menzies 2008; List and Menzies 2009, 2010).  We should attribute the effect to that property that is specific enough to suffice for it, but no more specific than that.