Value properties The
value of a physical object to an
agent is sometimes held to be supervenient upon the physical properties of the object. In
aesthetics, the
beauty of
La Grande Jatte might supervene on the physical composition of the painting (the specific
molecules that make up the painting), the artistic composition of the painting (in this case,
dots), the figures and forms of the painted image, or the painted canvas as a whole. In
ethics, the
goodness of an act of
charity might supervene on the physical properties of the agent, the mental state of the agent (his or her intention), or the external
state of affairs itself. Similarly, the overall suffering caused by an earthquake might supervene on the spatiotemporal entities that constituted it, the deaths it caused, or the natural disaster itself. The claim that moral properties are supervenient upon non-moral properties is called
moral supervenience.
Mental properties In
philosophy of mind, many philosophers make the general claim that the mental supervenes on the physical. In its most recent form this position derives from the work of
Donald Davidson, although in more rudimentary forms it had been advanced earlier by others. The claim can be taken in several senses, perhaps most simply in the sense that the mental
properties of a person are supervenient on their physical
properties. Then: • If two persons are indistinguishable in all of their physical properties, they must also be indistinguishable in all of their mental properties. An alternative claim, advanced especially by
John Haugeland, is a kind of
weak local supervenience claim; or, weaker still, mere
global supervenience. The claim that mental properties supervene globally on physical properties requires only a quite modest commitment: any difference between two possible worlds with respect to their instantiated mental properties entails at least
some difference in the physical properties instantiated in those two worlds. Importantly, it does
not require that the mental properties of an individual person supervene
only on that person's physical state. This weak global thesis is particularly important in the light of
direct reference theories, and
semantic externalism with regard to the content both of words and (more relevant to our concerns here) of
thoughts. Imagine two persons who are indistinguishable in their local physical properties. One has a dog in front of his eyes and the other has a dog-image artificially projected onto his retinae. It might be reasonable to say that the former is in the
mental state of seeing a dog (and of knowing that he does so), whereas the latter is not in such a state of seeing a dog (but falsely believes that he sees one). There is also discussion among philosophers about mental supervenience and our experience of duration. If all mental properties supervene only upon some physical properties at durationless moments, then it may be difficult to explain our experience of duration. The philosophical belief that mental and physical events exist as a series of durationless moments that lie between the physical past and the physical future is known as
presentism.
Computational properties There are several examples of supervenience to be found in
computer networking. For example, in a
dial-up internet connection, the audio signal on a phone line transports
IP packets between the user's computer and the
Internet service provider's computer. In this case, the arrangement of bytes in that packet supervenes on the physical properties of the phone signal. More generally, each layer of the
OSI Model of computer networking supervenes on the layers below it. We can find supervenience wherever a message is conveyed by a representational medium. When we see a letter "a" in a page of print, for example, the meaning
Latin lowercase "a" supervenes on the geometry of the boundary of the printed
glyph, which in turn supervenes on the ink deposition on the paper.
Biological properties In biological systems
phenotype can be said to supervene on
genotype. This is because any genotype encodes a finite set of unique phenotypes, but any given phenotype is not produced by a finite set of genotypes. Innumerable examples of
convergent evolution can be used to support this claim. Throughout nature, convergent evolution produces incredibly similar phenotypes from a diverse set of
taxa with fundamentally different genotypes underpinning the phenotypes. One example is
evolution on islands which is a remarkably predictable example of convergent evolution where the same phenotypes consistently evolve for the same reasons. Organisms released from predation tend to become larger, while organisms limited by food tend to become smaller. Yet there are almost infinite numbers of genetic changes that might lead to changes in body size. Another example of convergent evolution is the loss of sight that almost universally occurs in
cave fish living in lightless pools. Eyes are expensive, and in lightless cave pools there is little reason for fish to have eyes. Yet, despite the remarkably consistent convergent evolution producing sightless cave fish, the genetics that produce the loss of sight phenotype is different nearly every time. This is because phenotype supervenes on genotype. ==Arguments against supervenience-based formulations of physicalism==