 Another kind of counterexample to SCA, due to Johnston (1992) and Bird (1998), involves a fragile glass that is carefully protected by packing material. It is claimed that the glass is disposed to break when struck but, if struck, it wouldn’t break thanks to the work of the packing material. There is an important difference between this example and Martin’s: the packing material would prevent the breaking of the glass not by removing its disposition to break when struck but by blocking the process that would otherwise lead from striking to breaking. This difference will be important in the context of evaluating Lewis’s analysis of dispositions in  section 1.4.  The packing material is called a masker (Johnston) or antidote (Bird) to the glass’s disposition at issue (see Choi 2003 for a refinement of the masking counterexample to SCA).