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2.5 Are Bases ultimately Dispositional, or Non-dispositional?

Suppose we do follow the scientific method outlined above, and analyse observed dispositions in terms of constituents. Presumably the parts are to have the ability to interact. But this means at the microscopic level of explanation we again have to accept some kinds of dispositional properties: of the parts this time. This is because `to be able' signals a dispositional property. Thus I will argue (somewhat controversially) that in fact dispositional properties, though perhaps explained, are never explained away. However much we may dislike them, they are never found to be illusory, and cannot be completely replaced by talk of functional relationships, differential equations, and probability calculus. If we can understand dispositions, I will argue, then we will be able to understand a great deal of what nature is about.

It is a mistake, in fact, to think that the scientific explanations above have completely removed the need for dispositional properties of some kind. Look again at the cases of dispositional explanation outlined above.

The solubility of salt was explained by composition in terms of the ions Na+ and Cl-, and how these constituents interact with the H2O water molecules. A full explanation, however, has to explain that the Na+ and Cl- ions have an electric force between them, and this this force can be overcome by the greater attractions of the ions with the water molecules. The solubility of the salt depends not merely that there are the ions and molecules, but also on the dispositions of these constituents to interact with each other in complicated ways in all the various possible circumstances. Similarly, the explanation of the flexibility of a piece of metal in terms of the arrangement of the metal atoms depends on some forms of dispositions for for interaction between the atoms. The temperature of a substance can still be explained well in terms of the speeds of motion of the internal atoms and molecules, but without the (dispositional) ability of the atoms to elastically interact with each other and transfer momentum, `temperature' would be useless as a general term of description. `Dormative virtue' of opium finds explanation in terms of the effects of the morphine on the rate of release of neurotransmitters only because morphine has a disposition to interact with the appropriate brain chemicals.

Some dispositional phenomena in science, of course, have spectacularly resisted this kind of explanation in terms of parts.   Newton's gravitational attraction between all pairs of bodies is a dispositional property, as rule for acceleration of a given body a = GM/r2 states not what always does occur, but what would occur in suitable circumstances (e.g. if there were no other attracting bodies around anywhere). The gravitational attraction can be formulated as a force or as a potential field, and these bring out more clearly the dispositional nature of the phenomenon. We will discuss in chapter 3 the problems Newton had in trying to explain gravity. All we need to note now that gravity appears to be an example of a fundamental force which acts between all constituents, no matter how small, and therefore cannot be explained merely in terms of the relations between the constituents. Electric and magnetic forces pose worse problems.

At the microscopic level we might hope that the constituents have many definite properties (e.g. mass, shape, position, velocity, energy etc.), and only a few of those peculiar dispositional properties (e.g. perfect elasticity, gravitational attraction, and electric charge). In that way there might be a minimum number of these inexplicable `occult powers'. Such would be the case if Newtonian physics were true, as seen in chapter 3.

Quantum phenomena show, however, that this hope is not satisfied. We will see in chapter 4 how quantum physics has more kinds of dispositions than does Newtonian physics. For the properties of position and velocity, previously thought quite definite, now behave like dispositional properties that may or may not have definite values. This book will be working towards a `propensity interpretation' of quantum physics, according to which the quantum world contains very few non-dispositional properties, i.e. very few properties that always have perfectly definite values. In particular, it will turn out that there is no such thing as a definite corpuscle. Following Maxwell [1985], this concept is replaced by that of a `packet of propensity' or `propensiton'.

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Prof Ian Thompson


Author: I.J. Thompson (except as stated)