Supervenience

2. The promises and problems of supervenience

Once a supervenience claim is properly formulated and its strength suitably identified, it offers the seductive promise of a path between full-scale reduction of upper-level to lower-level properties, and an uncomfortable dualism. Full-scale reduction is here the attempt to show that there is really nothing but the underlying level, and that talk in upper-level terms merely makes disguised reference to this one kind of reality. It is prompted by metaphysical unease but it is expensive, since it usually turns out that the requisite reductions distort what we mean or what we are referring to. For example, it is highly unnatural to say that when we describe a computer by saying which programme it is running we either mean anything about its electronics or are referring to its engineering configuration. We are doing something different altogether, yet we ought to be able to make software descriptions metaphysically innocuous even if we think that all that is fundamentally going on is captured by the full story about the machine’s hardware. Allowing that the software characterization supervenes on the hardware may fulfil this promise. Supervenience promises the relief from metaphysical anxiety, but without the costs of reduction.

To fulfil this promise it is clear that we must understand why the impossibilities in question arise. Without such an understanding, the upper-level properties may still seem to be unexplained ‘danglers’ or unexplained arrivals on the scene (reduction at least promises this explanation, by collapsing the two levels into one). This in turn may be a useful constraint on philosophies of various areas: for example, understanding why (E) is true may be easier on some accounts of ethical commitment than others. But without such extra commentary, and in particular in the philosophy of mind and the philosophy of language, supervenience claims may easily be part of the problem rather than part of the solution (see Reductionism in the philosophy of mind).