Physicalism

Over at Philosophical Disqusitions, a few entries on Physicalism have appeared which begin by defining physicalism as the thesis that "all facts are physical facts".

The physicalist thesis cannot be anything like “all facts are physical facts”.   In what sense could a fact be physical?  

So stated, the definition makes a mockery of itself, for it points to one of the most central (and, puzzlingly, one of the least-discussed) problems with physicalism itself.  We so often hear about Mary the color-scientist, about zombies and about “qualia”, that we are lead to ignore a far more challenging difficulty for the physicalist.

For surely, what is meant by the physicalist’s doctrine is something like this: the objects and predicates referred to by genuine sentences are always physical objects and physical properties.  This is a far more useful definition of physicalism.  A paradigm case of a “genuine sentence” might be something like: “the temperature of boiling water on Earth is 100 Celcius”.  The objects (water, the planet Earth) and the predicates (temperature, 100 Celcius) can be given fully physical descriptions, presumably involving a particular molecular structure and mean kinetic energy of molecules.

When we confine ourselves to sentences like this, physicalism seems eminently plausible.  But, of course, there are many other types of sentences, even ones that appear regularly in the physical sciences, which are much more difficult to redescribe in the required way.

Take, for example, a sentence of mathematics like “1 plus 1 equals 2” or “A² plus B² equals C²”.  Or, perhaps a theoretical sentence like Einstein’s “the passage of time varies according to the observer’s frame of reference.”  Or even a philosophical sentence like “physicalism is true”.  Surely, the proponent of physicalism wants to be able to use sentences like this.  Yet, mathematical objects like numbers or variables and properties like equals leave us scratching our heads, searching for redescriptions that could possibly count as physical descriptions.  Similarly, terms like time, observer and (perhaps most troublingly) true resist this kind of redescription to an enormous degree.  Yet, these are sentences that must be valid ones, especially since they play central roles in the mature physical sciences, the very sciences whose success lead us to propose the idea of physicalism in the first place.

I think that this kind of problem itself deserves far more attention than it gets, and it is likely that it will reappear for any proposed definition of physicalism.