 Second, an example due to Douglas Ehring (1987). Jones puts some potassium salts into a hot fire. Because potassium compounds produce a purple flame when heated, the flame changes to a purple colour, though everything else remains the same. The purple flame ignites some flammable material nearby. Here we judge that putting the potassium salts in the fire caused the purple flame, which in turn caused the flammable material to ignite. But it seems implausible to judge that putting the potassium salts in the fire caused the flammable material to ignite.