View Supervenience
In philosophy, supervenience is a kind of dependency relationship, typically held to obtain between sets of properties. According to one standard definition, a set of properties A supervenes on a set of properties B, if and only if any two objects x and y which share all properties in B (are “B-indiscernible”) must also share all properties in A (are “A-indiscernible”). That is, A-properties supervene on B-properties if being B-indiscernible implies being A-indiscernible. The properties in B are called the base properties (or sometimes subjacent or subvenient properties), and the properties in A are called the supervenient properties. Equivalently, if two things differ in their supervenient properties then they must differ in their base properties. To give a somewhat simplified example, if psychological properties supervene on physical properties, then any two persons who are physically indistinguishable must also be psychologically indistinguishable; or equivalently, any two persons who are psychologically different (e.g., having different thoughts), must be physically different as well. Importantly, the reverse does not follow (supervenience is not symmetric): even if being the same physically implies being the same psychologically, two persons can be the same psychologically yet different physically: that is, psychological properties can be multiply realized in physical properties.
Supervenience has traditionally been used to describe relationships between sets of properties in a manner which does not imply a strong reductive relationship. For example, many hold that economic properties supervene on physical properties, in that if two worlds were exactly the same physically, they would also be the same economically. However, this does not entail that economics can be reduced in any straightforward way to physics. Thus, supervenience allows one to hold that “high-level phenomena” (like those of economics, psychology, or aesthetics) depend, ultimately, on physics, without assuming that one can study those high-level phenomena using means appropriate to physics.
Examples of supervenient properties:
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 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, 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, 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, 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.
Arguments against supervenience-based formulations of physicalism:
Although supervenience seems to be perfectly suited to explain the predictions of physicalism (i.e. the mental is dependent on the physical), there are four main problems with it. They are Ephiphenomenal ectoplasm, the lone ammonium molecule problem, modal status problem and the problem of necessary beings.
Epiphenomenal ectoplasm
Epiphenomenal ectoplasm was proposed by Horgan and Lewis in 1983, in which they stated, a possible world (a world that could possibly exist) W is identical to our world in the distribution of all mental and physical characteristics (i.e. they are identical), except world W contains an experience called epiphenomenal ectoplasm that does not causally interact with that world. If supervenience physicalism is true, then such a world could not exist because a physical duplicate of the actual world (the world that is known to exist) could not possess an epiphenomenal ectoplasm. This was rectified by Frank Jackson, by adjusting the application of supervenience within physicalism to state "Physicalism is true at a possible world W if and only if any world which is a minimal physical duplicate (i.e. identical) of W is a duplicate of W simpliciter."
The lone ammonia molecule problem
The lone ammonia molecule problem provides a problem for Jackson’s solution to epiphenomenal ectoplasm. It was proposed by Jaegwon Kim in 1993 when he stated that according to Jackson’s idea of supervenience, a possible world W was identical to the actual world, except it possessed an extra ammonia molecule on one of Saturn’s rings. This may not seem to provide much of a problem, but because Jackson’s solution refers only to minimal physical duplicates, this allows for the mental properties of W to be vastly different than in the actual world. If such a difference would cause mental differences on Earth, it would not be consistent with our understanding of physicalism.
Modal status problem
The modal status problem is only problematic if one thinks of physicalism as a contingent truth (i.e. not necessary), because it is described in terms of modal notions (i.e. through modal realism). The problem is presented when from the statement "Minimal physical truths entail all truths", one derives the statement "S (a statement that describes all minimal physical truths) entails S* (a statement that describes the world)". This statement is a necessary truth, and therefore supervenience physicalism could not be contingent. The solution to this is to accept the above statement not as the equivalent of physicalism, but as an entailment of it.
Problem of necessary beings
The problem of necessary beings was proposed by Jackson in 1998, in which he stated that a necessary being exists in all possible worlds as a non-physical entity, and therefore proves physicalism false. However, physicalism allows for the existence of necessary beings, because any minimal physical duplicate would have the same mental properties as the actual world. This however is paradoxical, based on the fact that physicalism both permits and prevents the existence of such beings. However, the existence of necessary beings is paradoxical in itself. They are both distinct from the physical world and dependent upon it. This violates Hume’s fork which states, "there are no necessary connections between distinct existences".
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