The glass vase on my desk is fragile. It should be handled with care because it it is likely to shatter or crack if it is knocked, dropped, or otherwise treated roughly. The vase has certain dispositions, for example the disposition to shatter when dropped. But what is this disposition? It seems on the one hand to be a perfectly real property, a genuine respect of similarity common to glass vases, china cups, ancient manuscripts, and anything else fragile. Yet on the other hand my vase’s disposition seems mysterious, “ethereal” (as Nelson Goodman (1954) put it) in a way that, say, its size and shape properties are not. For my vase’s disposition, it seems, has to do only with its possibly shattering in certain conditions, conditions which I hope will never be realized. In general, it seems that nothing about the actual behavior of an object is ever necessary for it to have the dispositions it has. Many objects differ from each other with respect to their dispositions in virtue of their merely possible behavior, and this is a mysterious way for objects to differ.
Much of the recent work on the topic of dispositions has been focused on attempts to dispel this mystery by explaining attributions of dispositions in other, more readily understandable terms. But even with such an explanation in hand, metaphysical questions about dispositions remain. One group of questions concerns the “grounds” or “bases” of dispositions: my glass vase is fragile, it seems, in virtue of its irregular atomic structure, and in that sense the atomic structure of the vase grounds its fragility. What exactly is the relation between dispositions, like fragility, and their grounds or bases, like my vase’s atomic structure? And need there always be a ground or basis to a disposition: might there be “bare” dispositions, ones not grounded in anything at all? Another metaphysical question about dispositions is whether they are (all) intrinsic properties, or whether instead they can be acquired and lost without any intrinsic change in their bearers. Finally, there is a question about the role of dispositions in causation: are dispositions causally efficacious properties, or are they instead epiphenomenal? . . . .