Ilmari Hirvonen (University of Helsinki), Ilkka Pättiniemi (University of Helsinki)
In their book Every Thing Must Go (2007, Oxford: OUP) James Ladyman and Don Ross defend modal realism, which we argue is in conflict with their programme of naturalistic metaphysics. Ladyman and Ross criticise empirically unconstrained metaphysics that they call strong metaphysics. This variety of metaphysics is, according to them, mainly motivated by wanting to give explanations in order to make some things or phenomena seem less mysterious. Ladyman and Ross contrast strong metaphysics with weak metaphysics, which is based on Kitcherian unification of special science hypotheses with ones from fundamental physics. Ladyman and Ross maintain that strong metaphysics should not be pursued whereas weak metaphysics is the only viable sort of metaphysics that there is or can be. We argue that Ladyman and Ross’ modal realism doesn’t do the unificatory work they claim is the only acceptable form of metaphysics. Additionally, their reasons for endorsing modal realism are either lacking or in tension with their critique of strong metaphysics.
Ladyman and Ross present three reasons for accepting modal realism. First, modal expressions are used in science, and at least some modal claims are considered to be theory-independently true. The second reason is a new version of the traditional no-miracles argument. Ladyman and Ross’ branch of realism focuses on the modal or nomological relations within scientific theories. They claim that without objective modal structures such standard features of scientific practice as successful theory conjunction and novel prediction would be entirely mysterious. Third, and lastly, modal realism justifies inductive generalisations.
Concerning the first argument it must be acknowledged that Ladyman and Ross are right when they claim that modal terminology is indeed indispensable in science. However, the usage of such language does not yet, in itself, bind us to a realist interpretation of it. Hence, it is not clear how strong of an ontology the lexicon we have endorsed binds us to. At the very least, Ladyman and Ross should offer an argument for the conclusion that modal expressions necessarily force us to accept modal realism, and this is something they have not yet done. Ladyman and Ross’ second and third arguments are motivated by offering an explanation for something that would otherwise seem mysterious or miraculous, and this is precisely the kind of motivation for metaphysics that they oppose.
The third argument seems to lead Ladyman and Ross on the path of strong metaphysics because induction is needed already in fundamental physics. So modal realism is required to justify induction before any unificationary work is done between fundamental physics and the special sciences. Therefore, instead of being weak unificatory metaphysics, modal realism seems to be some kind of a transcendental condition for empirical science. This seems to be a clear indication of strong metaphysics.
We claim that in the end Ladyman and Ross have to face the following dilemma: either they must accept that they participate in strong metaphysics, or dilute their modal realism to the point of indistinguishability from empiricist antirealism.
