Powerful properties and the causal basis of dispositions

International audienceMany predicates are dispositional. Some show this by a suffix like “-ible”, -uble”, or “-able”: sugar is soluble in water, gasoline is flammable. Others have no such suffix and don’t wear their dispositionality on their sleeves. Yet part of what it is to be solid is to be disposed to resist deformation, and part of what it is to be red is to appear red to normal human observers in normal lighting conditions. However, there is no agreement as to whether dispositional predicates may be given a realist interpretation. For many authors, propositions containing them are made true by states of affairs (or facts) containing categorical, rather than dispositional properties. Many also claim that the states of affairs that make true attributions of dispositions to macroscopic objects are microscopic states of affairs concerning their parts. For example, what makes a vase fragile is the microscopic structure of its molecular constituents, which is what makes the vase break when it falls.Against these claims, I will argue that what makes a dispositional predicate apply to an object, whether macroscopic or microscopic, whether in common sense or science, is the object’s having what I will call a powerful property. If the object is macroscopic, it is another matter whether the property is microreducible. My reasons for supposing that these powerful properties exist are those for postulating theoretical properties generally: they unify existing explanations and suggest new ones.My plan is as follows. I will begin with a brief sketch of the debate between what I call the reductionist and the realist doctrines about dispositions. Then I will argue that there are many so-called multi-track dispositions, both in common sense and in science, and that accounting for them requires a distinction between the concepts of powerful property and disposition. I will give three examples of multi-track dispositions, one from common sense, one from physics and one from cognitive psychology. In each case in which an object has a multi-track disposition, it has a powerful property that contributes causally to bring about the manifestations of the disposition. The distinction between powerful properties and dispositions makes realism and reductionism compatible: Realism is justified with respect to powerful properties, whereas the ascription of a disposition is reducible: it is made true by the fact that the object has a powerful property, together with laws of nature. I will then justify the existence of real powerful properties against several arguments: that such properties are pseudo-properties having only verbal existence, that only their reduction base is causally efficacious and therefore real, that some dispositions need no such causal basis, and that there are no irreducible multi-track dispositions in the first place