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In philosophy, supervenience is arguably defined as a dependency relation between 'higher-level' (e.g. mental) and 'lower-level' (e.g. physical) properties.
Informally, a group of properties X supervenes on (alternatively, is supervenient on) a group of properties Y exactly when the X-group properties are determined by the Y-group properties, where "determined by" is taken non-specifically.
Formally, X-group properties supervene on Y-group properties if and only if either of the following holds for all objects a and b:
- a and b cannot differ in their X-group properties without also differing in their Y-group properties.
- If a and b have identical Y-group properties, then they also have identical X-group properties.
- If a and b do not have identical X-group properties, then they also do not have identical Y-group properties.
(All of these formulations are logically equivalent, so if one of them holds, all of them do.)
Examples
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 state of affairs itself. Similarly, the overall suffering caused by an earthquake might supervene on the spatio-temporal entities that constituted it, the deaths it caused, or the natural disaster itself.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. The simplest is perhaps as the claim that the mental properties of a person is supervenient on their physical ''properties'. Then:- If two people, X and Y, are identical with regards to their physical properties, they must also be identical in their mental properties.
- If two people, X and Y, are identical with regards to their mental properties, they must also be identical in their physical properties.
An alternative claim, advanced especially by John Haugeland, is the claim of "weak supervenience" or, at its weakest, "global supervenience". To claim that mental properties globally supervene on physical properties is to claim, merely, that a change between two possible worlds with respect to their instantiated mental properties requires some change in the physical properties instantiated in at least one of those two worlds. Importantly, it does not claim that the mental properties of an individual person supervene only on that person's physical state.
The latter, weaker 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 physically identical people, one of them looking at a dog and the other having a dog-image projected onto his retinae. It might be reasonable to say that the former is in the mental state of perceiving a dog, whereas the latter is not and merely (falsely) believes that he is.
There is also discussion amongst 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 seem difficult to explain our experience of duration. The philosophical belief that mental and physical events exist at a series of durationless moments that lie between the physical past and the physical future is known as presentism, and is a form of belief in Galilean relativity.
Computational Properties
There are several examples of supervenience to be found in computer networking. For example, note that in a dial-up internet connection, an audio signal in 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 physics of the phone signal. More generally, each layer of the OSI Model of computer networking supervenes on the layers below it.These computer examples exemplify a more general principle: we will 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.
See also
External links
"Supervenience"