 Based dispositions are dispositions with causal bases that are distinct from the dispositions themselves. Assuming that the glass’s microstructural property is a causal basis for and is distinct from its fragility, its fragility is a based disposition. As noted earlier, the possibility that a disposition serves as a causal basis for itself is not ruled out by the definitions of causal basis like PPJ or Lewis’s, in which case, the disposition is not a based disposition as it is not distinct from its causal basis. The requirement that a disposition be distinct from its causal basis should be carefully understood: it should not be interpreted to rule out causal bases that are only contingently identical to the corresponding dispositions. Based dispositions are dispositions with causal bases that are not necessarily identical to the dispositions themselves, in which sense they have distinct causal bases. When a disposition serves as a causal basis for itself, it is necessarily identical to its causal basis, which entails that it is not a based disposition. It might be thought, though, that a based disposition is contingently identical to its causal basis. In fact, Armstrong (Armstrong, Martin &amp; Place 1996) is well known for his claim that all based dispositions are contingently identical to their bases (cf. see  section 4.2  below). Bare dispositions are baseless dispositions, which means that they are dispositions with no distinct causal bases (McKitrick 2003b). See Johnston 1992, Smith &amp; Stoljar 1998, and Williams 2011 for different definitions of bare disposition.