For various reasons I was playing around with ways of summarising what is distinctive about Lewis’s contributions to philosophy, and I thought the following idea sounded interesting. I’m not sure whether it also sounds true, but I thought I’d put it forward for consideration.
One of the signature tasks of philosophy is to figure out the relationship between science and common sense. By ‘common sense’ here we don’t mean platitudes that people utter, as much as the tacit knowledge that lets us navigate the world successfully without sufficient explicit knowledge to pass any given tenth grade science course. Making that tacit knowledge explicit is one of philosophy’s tasks, and one at which Lewis excelled, but perhaps less crucial than relating it to the scientific image. Four options stand out here.
First, we could say that science has shown that common sense is badly wrong, and in need of radical overhaul. This way lies eliminitivism.
Second, we could say that common sense shows that science is either wrong or, at the very least, incomplete. Various forms of dualism and idealism lie this way.
Those two options say there is a tension between science and common sense. The next two options are for reconcilation.
So third, we could say that proper appreciation of science as we find it reveals a place for our common sense concepts. Various forms of naturalism, at least as that term is understood in America, go this way.
Lewis promoted, and to a large extent pioneered, a fourth way. By investigating the structure of common sense closely, we find that it is fit to be reconciled with science, almost any way that science turns out will turn out to be compatible with common sense.
This kind of approach, if it works, allows you to keep two of Lewis’s distinctive attitudes, attitudes he often displayed side by side. First, it’s not an open scientific question whether there are, say, psychological states such as beliefs and desires. Second, philosophy can’t overturn what science shows us. If we go with option three (not to mention option one), there is a danger that science will overturn tacit folk knowledge. That would be bad. If we go with option two, we’ll be using philosophy to overturn science. That would be worse. So option four it is.
The trick then is to make common sense fit for science, roughly however that science turns out to go. Lewis’s strategy here has three parts.
First, show that the ontological and ideological commitments of common sense (or at least the bits of common sense we are committed to keeping) are thin enough that science is guaranteed to meet them.
Second, provide a broadly functional analysis of common sense concepts, passing the question of what realises those functional roles to science. The functional roles are specified in a Wittgensteinian ‘near-enough-is-good-enough’ way, so as to maximise the chance that science will find realisers. (I don’t distinguish here between theories that provide functional definitions of folk terms, theories that provide rigidified functional definitions, and theories that take functional roles to be reference fixers, though that’s something we’d like to know when we do the details.)
Third, provide a broadly subjectivist account of those folk concepts that don’t look like science will find distinctive realisers for them. Lewis’s subjectivism about ethics and contextualism about epistemology fit into this part of the project.
At every stage the devil is in the details, but we can see a way to carry out option four in this outline. A large percentage of Lewis’s work can be seen as carrying out this three-step plan.
If this is the right picture in outline, then these paragraphs would be an introduction to a work saying how Lewis carried this off. That work would probably be book length, so I won’t try it here. But I wonder what people think of the broad story?