Next: 2.4 Scientific Explanation of Up: 2. Dispositions Previous: 2.2 Derivative Dispositions
It seems that dispositions are real properties of the things which have them. Before going on to look at the scientific explanation of dispositions, I want to consider some possible philosophical reasons for doubting the reality of dispositions. We might find force, for example, in one or more of the following objections: (a) that one should deny the subjunctive in the power ascription as anything more than hypothetical, (b) science should be content with finding only the regularity of effects, and not try to discover causes and determining constitutions, (c) that causes are only (previous) events and not powers & dispositions, or (d) that the world should be considered as a `Zeno universe' that has only successive states and no proper changes.
Taking approach (a), Ryle (, ch. 5) denies that dispositional ascriptions `assert extra matters of fact' and claims that they are only `inference-tickets, the minimal dispositions which licence us to predict, retrodict, etc.' That is, he would omit any `in virtue of the constitution of S' phrase in the meaning of dispositions, and, in a sense, make dispositions strange kind of things `no more substantial than a promise' (as Herbert  puts it). Since then, there is no property of S which makes the ascription true, that truth cannot be explained by properties of S. Thus Ryle (quite explicitly) denies that one should even look for either causal or mechanistic explanations of the dispositions. Even, presumably, in cases in physics and chemistry where there are quite obviously explanations in terms of constituents and their propensities to attract and repel each other. His restriction on looking for explanations in terms of internal dynamics is largely disregarded in scientific practice.
Concerning injunction (b), I accept that all observations are of effects rather than of causes, but that does not mean we cannot conceive of causes and of the way they might lead to effects. It seems to me quite legitimate for causes to be postulated in a Popperian fashion, and the consequences deduced for the production of effects. The reverse induction is quite different : obviously we cannot deduce precise causes from observable effects (as Hume has long pointed out), but that does not mean that there no causes. It should not be necessary to accept Hume's  conclusion that ``the distinction, which we often make between a power and the exercise of it, is without foundation''.
The attitude of (c) has been taken by Davidson , when he argues that causality is a two-place relation between individual events. Thus causal relations are certainly not just implications from the description of the first event to that of the second event, but are something more real. The reality of causality, however, does not thereby automatically include such components as dispositions and propensities, although Steiner  wants to extend Davidson's ideas in this direction. I want to allow both dispositions and previous events to be causes, although in different senses.
A distinction thus ought to be made between the `Principal Cause' (that disposition which operates), and the `Instrumental Cause' (that circumstance by means of which dispositions operate). Principal causes operate according to instrumental causes. Both are necessary for any event, for example, when a stone is let fall: the principal cause is the earth's gravitational attraction, and the instrumental cause is our action of letting go. Its hitting the ground is thus caused by our letting go, but only as an instrumental cause. Many common uses of `cause' (including that of Davidson ) refer to instrumental causes rather than principal causes, as it is only in the instrumental sense that events can be said to be causes. Previous events cannot be efficacious causes, Emmet  points out, in the sense of `producing' or `giving rise to' their effects. Davidson would argue that that the `onslaught' (i.e. the beginning) of a state or disposition is an event: `a desire to hurt your feelings may spring up at the moment you anger me; I may start wanting to eat a melon just when I see one.'2.4 That commencement event could then be regarded as the event which is the cause of the effects of the dispositions and desires. The difficulty with this argument is that only some, but not all, dispositions have initiating events of this kind. It is difficult, for example, to pinpoint the events which initiated the gravitational disposition of the earth, and the solubility of salt. In these instances, as elsewhere, it makes more sense to give a (principal) causal capacity to the dispositions themselves.
To consider (d) the world as a `block universe' or `Zeno universe', as recently pointed out by Emmet , is to see only different states of affairs at successive times, and not to see the changes that lead to these differences. Since the rise of Einsteinian relativity, it has become popular to see all of time and space in one `block continuum' of four dimensions, and to see change as only the difference between successive `time slices' of this continuum. In this world there is only what actually happens, and as in (a) above, what `might have happened' is purely hypothetical. The only sense of `might happen' that can be invoked is to imagine an entirely new possible world, e.g. one with different initial conditions or different physical laws. This world view thus does not base power ascriptions on any real features of this particular universe.
If we reject the `block universe' account of time, we are also rejecting the view of time in which the future is `already formed' and perfectly definite in advance of its happening, if indeed on this account anything happens at all. (In extreme versions of this theory, time and real change are both completely illusory, but Grünbaum (, ch. 10) shows that more moderate positions can be held.) I admit that these accounts have an internal consistency that makes them difficult to refute, but despite their being advocated by many philosophers and physicists since Minkowski, I do not believe that they should be the only coherent metaphysical systems on offer. In chapter 8 it will be seen that alternatives can be devised that not only have more explanatory power (e.g. for quantum physics, as in chapter 10), but also more practical use (see below, end of this section). Once these alternatives have been formulated, we should be able to judge in which way our world is most adequately described.It does in any case seem very odd to deny that objects have dispositional properties that relate what might happen as well as what actually happens. To deny causes apart from their manifestations, Mellor [1974 p. 173] shows, leads to some bizarre consequences, for then a disposition could not be ascribed when its operation is impossible. Taking precautions to avoid the conditions in which nuclear fuel would explode, to use his example, should not mean that the fuel was not explosive. `It is ridiculous to say that their success robs the fuel of its explosive disposition and thus the precautions of their point.'
Furthermore, a theory that only predicted what actually happens, and not what might happen, would be useless as an engineering planning tool. For it would not be able to predict the consequences of a plan that we might consider employing, but in the end did not actually use. Such a theory could not tell us, for example, what would have happened if one of the unsuccessful channel-tunnel designs had been chosen. These questions are of great practical (and political) importance, and, as we shall see in the next chapter, real physical theories are of course most useful here.
Next: 2.4 Scientific Explanation of Up: 2. Dispositions Previous: 2.2 Derivative Dispositions Prof Ian Thompson