Properties and Conditionals
The distinction between qualities and powers is often drawn by saying that ascriptions of powers, but not of qualities, entail certain kinds of counterfactual conditionals (Carnap 1936)-; Goodman 1954; Mumford 1998; Choi 2008). Hugh Mellor (1974) objects, saying that ascriptions of qualities also entail conditionals. For instance, ‘a is a triangle’ entails ‘if its corners were counted the answer would be three’. However, even though it is admitted that qualities also entail conditionals, our understanding of the quality in question seems to be independent of our understanding of any such entailment, while our understanding of a power appears to be dependent on our understanding of the entailment. We are able to understand what it is to be a triangle without knowing that its angle sum, if measured, is 180°. But we cannot understand what it is to be fragile without understanding that a fragile object would break if struck smartly. In this case, the conditional appears to provide the defining features of the power—what it is—while for qualities the conditional only spells out a consequence implied by the defining features that we are already acquainted with and understand. We understand a priori of actually counting that a triangle has three corners, but we do not understand what it is for something to be fragile a priori of experiencing something breaking easily. This implies that we somehow understand powers only through the conditionals, but that we have some other independent means to understand qualities. Note now, that the only qualities we can pretend to understand in this independent way are the ones we can perceive. It is only those features of reality of which we have sensible ideas, such as colours, smells, shapes, etc., that we can pretend to understand independently of any conditional that might be given. None of the properties discovered and described by science, but which we have no corresponding perception of, can be understood independently of conditionals of some sort.
However, it is also the case that of all the different sensible ideas we have, very few of them allow us really to infer much about the behaviour of the object we perceive to have the quality. We can perceive the smell of a wine, but what can we infer from that about the behaviour of the wine except how it will affect us? Spatial properties, the kind of properties on which perception and science agree, are an interesting exception. Shape is the best case there is for the identity of qualities and powers. We can arguably understand from our grasp of shapes, a priori of testing any particular shape, that a key fits in the appropriate lock in a way that no key with a different shape will do; we understand that a leaden ball dropped onto a pillow will make a hollow corresponding to whatever shape the ball happens to have. Indeed, Ingvar Johansson argues that we can ‘intuit [...] a kinematics of mechanisms in the same way as we can intuit some truths in Euclidean geometry’ (1997: 411). His point, I take it, is that Archimedes didn’t have to build an Archimedean screw to know it would work. He could see that it had to work merely on the basis of the visual representation of the geometry of the mechanism. If this is true, then we have in our grasp of shapes, a grasp of how quality and power go hand in hand. That is perhaps why engineering is such a successful and practical discipline.
Counterexamples have been given to show that shapes do not have a causal role, but they are inconclusive. For instance, Jonathan Lowe has suggested in conversation that a spherical soap bubble does not thereby have the power to roll on an inclined plane, which it should if its sphericity bestowed on it a distinctive causal role. Also, that regions of empty space have a shape but do not thereby influence anything in any distinctive ways.
The soap bubble is problematic for the purist who thinks powers are necessarily tied to particular manifestation properties, but not for the powerful qualities view. Adherents of the latter will say that, while the property contributes in the same way always, it will produce different outcomes depending on what it is interacting with on a given occasion. Take a standard ball from a pinball machine and submit it to a range of experimental conditions, say, testing it on a range of different automated pinball machines with a range of surfaces, including magnetic and sticky toffee surfaces. The shape of the ball will in each of these conditions contribute to the outcome, but the ball will not behave the same because different powers will be jointly contributing in each case. Furthermore, it will behave differently in each condition compared to balls with a different shape (all other properties being equal); the difference will be down to the difference in shape. Replace the pinballs with soap bubbles with different shapes and the soap bubbles will behave very differently from the pinballs, mostly for reasons having nothing to do with their shapes, but the difference between the behaviour of spherical and non-spherical soap bubbles would be down to shape if that were the only difference in properties.
As for the empty sub-regions of space, they simply are not distinct objects that bear property instances of any kind independently of the rest of space, and so should not be expected to have any distinct causal powers of their own.