I’ve been reading a bit of David Lewis recently, one point he makes early on in his work “On the Plurality of Worlds”, is that the utility of a theory is a reason for accepting that it is true. The non-philosophical example he gives is in set theory, construct your sets and ontology however way which you want, and you get out what you want, by determinedly deciding one’s axioms and the conditions in which one may establish a theorem or establish some proof or impossibility by way of reductio.
Lewis quotes a phrase (apparently) from Hilbert, which goes something like “Set theory is a mathematician’s paradise”; likewise, we may also have a metaphysician’s paradise by way of thinking within the jargon of modal realism; of possibilia, logical space, closeness of worlds, while many object to the proposal of modal realism, the very fact that people still talk about it, and use the terminology of worlds, counterparts, and so on; is a testimony to the influence and power of this thesis.
While one has critical thoughts about this thesis (concerning isolation and the knowledge of worlds); there is an underlying appeal which must be taken seriously. Philosophy considered as establishing theories that balances a strength of a theory against its weakness. What are strong aspects to a theory? By theory, I mean not just metaphysical theories, but scientific theories, or even moral or empirical hypotheses as well.
A theory may have strengths in virtue of the following things:
1. Theoretical unity, interconnectedness
4. Confirmable predictions
5. Upgrading past theories
6. Refuting contemporamous competing theories
7. Being formalised, mathematicised
A theory, while emphasising one of these things, may also have a cost:
1. Being empirically false
2. Being non-empirical
3. Being inapplicable to higher genera concepts
4. Invoking weird ontologies
5. Violating parsimony
6. Incommensurability (ie. an incompatibility with other theories, or no address of corollorary issues)
7. Not having any predictive power
The spirit of utility arguments is that they are not so much arguments but appeals to truth. With utility one does not argue that something is or is not the case, as such, as in a formal deductive argument, but one appeals to the truth of something by its utility; to force the in another way: no other theories explain as much as this does; or if it does, then it is a better theory.
If we pursued this kind of line of metaphysics, we would have two implications:
1. Arguments are not so easy to knock down (hopefully); if we establish a thesis by many prongs, taking one prong away does not take away the thesis. This means we can concede to criticisms without complete abandonment and philosophy becomes essentially a concilatory project of theories and different metaphysical topics.
2. Philosophy would truly work in the old way of being systematic; we can show how one discourse relates to another; we may simultaneously be doing philosophy of mind and metaphysics; epistemology and philosophy of science; philosophy of mind and metaethics. Perhaps this issues would be more muddied up, admittedly, but we may find the age of the big systems arriving again. Lewis, in one’s eyes, is a systematic philosopher; but not one par excellence.