E-014 SEP Physicalism - Supervenience Intuition (Excerpt)

Exact excerpt

> A dot-matrix picture has global properties — it is symmetrical, it is cluttered, and whatnot — and yet all there is to the picture is dots and non-dots at each point of the matrix. The global properties are nothing but patterns in the dots. They supervene: no two pictures could differ in their global properties without differing, somewhere, in whether there is or there isn’t a dot (1986, p. 14). 
This gives us one way to think about the basic idea of physicalism. The basic idea is that the physical features of the world are like the dots in the picture, and the psychological or biological or social features of the world are like the global properties of the picture. Just as the global features of the picture supervene on the dots, so too everything supervenes on the physical, if physicalism is true.
It is desirable to have a more explicit statement of physicalism, and here too Lewis’s example gives us direction. He says that, in the case of the picture, supervenience means that “no two pictures can be identical in the arrangement of dots but different in their global properties”. Similarly, one might say that, in the case of physicalism, no two possible worlds can be identical in their physical properties but differ, somewhere, in their mental, social or biological properties. To weaken this slightly, we might say that if physicalism is the case at _our_ world – that is, is true of our universe and everything in it – then no _other_ world can be physically identical to our world without being identical to it in all respects. This suggests the following general account of what physicalism is (in the following formulation and in subsequent ones, we use “iff” to abbreviate “if and only if”): 
 
(1)
     Physicalism is true at a possible world _w_ iff any world which is a physical duplicate of _w_ is a duplicate of _w_ _simpliciter_.
If physicalism is construed along the lines suggested in (1), we have an answer to the completeness question. The completeness question asks: what relation does everything bear to the physical if physicalism is true? According to (1), the answer is that everything must supervene on the physical; or, to put it more technically, there is no possible world which is identical to our world in every physical respect but which is not identical to it in a biological or social or psychological respect. It will be useful to have a name for physicalism so defined, so let us call it _supervenience physicalism_. 
Supervenience offers one modal formulation of physicalism, but it is worth taking note of a second modal formulation too. Suppose we say that a property _G_ is necessitated by a property _F_ just in case, in all possible worlds, if something is _F_ then it is _G_ ; in this sense, for example, being red necessitates being colored, and being square necessitates having some extension in space. This suggests a formulation of physicalism along the following lines: 
 
(2)
     Physicalism is true at a possible world _w_ iff every property instantiated at _w_ is necessitated by a physical property.
What is the relation between physicalism so defined, which we might call _necessity physicalism_ , and _supervenience physicalism_? At least if necessitation is understood as a sort of entailment, then these are not equivalent; for discussion of this point, see [supervenience](https://plato.stanford.edu/entries/supervenience/). However, (1) and (2) are clearly similar, in particular they are modal formulations of physicalism. In what follows we will concentrate on supervenience physicalism, but what we will say will apply also to necessity physicalism.

Where on the page

Physicalism - section 2.1 (approx line 118).