DO VERIFIED CONSEQUENCES PROVIDE A BASIS FOR HOLISM?
A particularism such as Mill, wants to say that there is evidence for a theory consisting of a set of laws (evidence that provides a good reason for believing the theory) if and only if there is evidence for each law in the theory, and consequences derived from and explained by the theory are verified.
How is the second condition to be understood? Do the verified consequences of the theory provide evidence for the theory? If the particularist says that they do, then since they are derived and explained by a combination of assumptions in the theory, perhaps even all of them, the holist will accuse the par- ticularist of creeping holism. If these verified consequences are derived using all the assumptions of the theory, then they provide evidence for the whole theory, not for parts of it.There are several replies a particularist like Mill will make. First, verified consequences are frequently derived from some, but not all, of the assumptions of a theory. Second, the fact that a consequence of a theory has been derived and verified is not by itself necessarily evidence for the theory. The basic assumptions of the theory may have no causal-inductive support, and if not, the idea that verified consequences provide support is subject to the competing hypothesis objection (in its acceptable version).[126] Third, and most important, before accepting the charge of creeping holism, Mill will say, you need to look at the verified consequences to see what, if anything, they do support. Let me explain by reference again to the wave theory.
During the 1840s, when Mill and Whewell were debating, the wave theory included basic assumptions such as these: light is a wave motion, not a stream of particles emanating from luminescent bodies; the wave motion exists in a highly elastic substance called the ether; the waves move in a direction perpendicular to the wave front; they can interfere constructively or destructively, depending on whether their phases coincide
204 | SPECULATION: WITHIN AND ABOUT SCIENCE or cancel; and so on.
One of the established consequences of the wave theory, which is explained by that theory, is that light moves in straight lines. But, Mill would insist, contrary to holism, it is explained by the theory by appeal not to the entire theory but only to a part of it that claims that light waves in the ether move in a direction perpendicular to the wave front.More important, however, Mill would ask, “Does the established fact that light moves in straight lines constitute evidence even for the theoretical assumption that light waves in the ether move in a direction perpendicular to the wave front?” Mill would say that it could if there were causal and inductive support for the assumption that there exists an ether in which the putative waves wave. You can't have waves without some substance waving—at least that is a basic idea behind the wave theory in the mid-nineteenth century. So at best, the fact that light travels in straight lines, or that there are interference effects of the sort observed by Young and Fresnel, constitute evidence only for the conditional: if light consists of waves in the ether, then these waves travel in a direction perpendicular to the wave front, they interfere constructively and destructively, etc.
Mill would give the same response to Maxwell's 1860 kinetic-molecular theory of gases. For example, the fact that a malodorous gas such as hydrogen sulfide introduced at one end of the room takes some time to be detected at the other end was taken as evidence that gas molecules do not move freely from one end of the room to the other but collide with other molecules. Mill would say: “this observed phenomenon is not evidence that moving molecules collide, but only that if moving molecules exist then they collide.” Indeed, Maxwell himself suggests as much when in 1859 he writes to Stokes, admitting his theory is a “speculation” and saying
Now do you think that there is any so complete a refutation of this theory of gases as would make it absurd to investigate it further so as to found arguments upon measurements of strictly “molecular” quantities before we know whether there be any molecules?[127]
In the next section, I will formulate this idea more generally (an idea that I think Mill as well as Maxwell regard as important, and justly so).
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