Professor Stoljar is the author of the article called “Physicalism” in the Stanford Encyclopedia of Philosophy. In that article, he explains that physicalism is the metaphysical view that everything in the universe is physical or material, i.e. that there is nothing in the world except stuff like matter and energy and arrangements of such stuff. This is opposed to other views, like the ancient claim by Thales that everything is made of water, or the more modern theory of Bishop Berkeley, who said that all of reality is mental. A physicalist, in particular, will deny that there are minds or souls that exist somehow independently of people’s living bodies.
In his book called Physicalism, however, Stoljar argues that there is no way to state the doctrine of physicalism that will result in a view that is both physicalistic (“physicalism that deserves the name”) and true. Either we have to broaden our definition of “physicalism”, in which case it’s not really physicalism anymore, or we have to restrict our definition, in which case the world isn’t completely physicalistic.
Stoljar presents lots of arguments for and against his position in great detail (too much detail for me anyway). The conclusion I reached, however, is that although it is difficult to offer a precise definition of physicalism that can deal with every imaginable counter-example (e.g. physics in an alternate universe), it is sufficiently clear what the physicalist position is. Scientists have been investigating the nature of reality at low levels (the subatomic) and high levels (the intergalactic) and cataloging what they’ve found. So far it seems that everything is made up of certain kinds of stuff (photons, quarks, dark energy, strings, whatever).
The physicalist view is that there’s nothing else floating around, in particular, no mental substances, souls, angels or unattached ideas. Stoljar says we can’t sensibly explain physicalism in terms of what there isn’t (he calls this the via negativa), but it seems to me that we can. The list of non-physicalistic things that we need to mention (e.g. souls and mental substances) is not as long as Stoljar suggests. (1/2/12)