Supervenience

Supervenience

There is supervenience when and only when there cannot be a difference of some sort A (for example, mental) without a difference of some sort B (for example, physical). When there cannot be an A-difference without a B-difference, then but only then A-respects supervene on B-respects.

Supervenience claims are thus modal claims. They are claims to the effect that necessarily, there is exact similarity in A-respects whenever there is exact similarity in B-respects.

So if, for example,mental properties supervene on physical properties, then, necessarily, individuals that are physically indiscernible (exactly alike with respect to every physical property) are mentally indiscernible (exactly alike with respect to every mental property).

physically indiscernible

Thus, A-properties supervene on B-properties just in case how something is with respect to A-properties is a function of how it is with respect to B-properties.

Supervenience has been invoked in nearly every area of analytical philosophy. In addition to its having been claimed that mental properties supervene on physical properties, it has also been claimed that normative properties—moral, aesthetic, epistemic, and so on—supervene on natural properties, that general truths supervene on particular truths, and that modal truths supervene on nonmodal truths.

Supervenience, moreover, has been used to distinguish various kinds of internalism and externalism: epistemic, semantic, and mental. And it has been invoked to test claims of reducibility and claims of conceptual analysis, both of which entail supervenience claims.

conceptual analysis

Much of the philosophical work on supervenience itself, as opposed to its philosophical applications, has focused on distinguishing various varieties of supervenience, and examining their pairwise logical relations.

But, before turning to the main varieties of supervenience, we can make some central points working just with the idea that there cannot be an A-difference without a B-difference.

1. Model force

The term cannot in a supervenience claim can express logical impossibility, nomological impossibility (impossibility by virtue of laws of nature), or some other kind of impossibility.

Model force

If it is logically impossible for there to be an A-difference without a B-difference, then A-properties logically supervene on B-properties; if that is only nomologically impossible, then there is merely nomological supervenience.

The property being a bachelor logically supervenes on the set of properties {being unmarried, being a man} because it is logically impossible for individuals to differ with respect to being a bachelor without differing with respect to some property in that set.

According to the Wiedemann-Franz law, the electrical conductivity of metals covaries with their thermal conductivity; thus, in metals, electrical-conductivity properties nomologically supervene on thermal conductivity properties (and vice versa).

2. The relata of the supervenience relation

The relata of the supervenience relation

A difference can be a difference in any respect in which there can be a difference: a difference with respect to what properties something has, in what truths hold, in what conditions obtain, in what events occur, in what laws of nature there are, and so on.

The relata of the supervenience relation thus seem many and varied. Indeed in “There cannot be an A-difference without a B-difference,” A and B may range over nearly all manner of entities.

It is often claimed, however, that nonempty sets of properties are the primary relata of the supervenience relation: either A-respects and B-respects will be properties in some nonempty sets of properties A and B, or else A-respects will supervene on B-respects in virtue of A-properties supervening on B-properties.

conception of properties

This view requires an “abundant” (as opposed to a “sparse”) conception of properties, according to which properties “may be as extrinsic, as gruesomely gerrymandered, as miscellaneously disjunctive, as you please.... [They] far outrun the predicates of any language we could possibly possess.... In fact, the properties are as abundant as the sets themselves, because for any set whatever, there is the property of belong to that set”.

3. Logical properties of the supervenience relation

Supervenience is reflexive, transitive, and nonsymmetric. Trivially, it holds when A = B and so is reflexive. It is also transitive, because if there cannot be an A-difference without a B-difference, and cannot be a B-difference without a C-difference, then there cannot be an A-difference without a C-difference.

However, it is neither symmetric nor asymmetric, and so is nonsymmetric. Every reflexive case of supervenience is trivially symmetric. But, for instance, being a bachelor asymmetrically supervenes on {being unmarried, being a man}.

Logical properties of the supervenience relation

James is a man and Vanessa is not, and so they differ with respect to B-properties. But since James is married, they are exactly alike with respect to being a bachelor: neither of them has that property.

4. Supervenience and entailment

A notion of property entailment can be defined as follows: property P entails property Q if and only if it is logically necessary that whatever has P has Q. Supervenience shares with entailment the properties of being reflexive, transitive, and nonsymmetric.

Property supervenience, however, is neither necessary nor sufficient for property entailment. The property being a brother entails the property being a sibling.

Supervenience and entailment

But being a sibling does not supervene on being a brother. Thus, suppose that Sarah has a sister and that Jack is an only child. Then Sarah is a sibling and Jack is not, though neither is a brother. Property entailment thus does not suffice for supervenience.

It is often claimed in the literature that logical supervenience suffices for entailment (see, for example, Chalmers 1996). But that is not in general true. If A = {P&Q} and B = {P, Q}, then the A-property logically supervenes on B-properties, but no B-property entails the A- property.

Indeed, every property F will supervene with logical necessity on its complement, not-F: Two things cannot differ with respect to F without differing with respect to not-F (and vice versa). But of course being F does not entail being not-F (McLaughlin 1995).

5. Supervenience and ontological priority

Supervenience and ontological priority

Many of the most interesting cases of supervenience are ones in which the subvenient factors are ontologically prior to the supervenient factors. Supervenience itself, however, is not an ontological priority relation.

Ontological priority is irreflexive and asymmetric: Nothing can be ontologically prior to itself or be ontologically prior to something that is ontologically prior to it. But supervenience is reflexive and not asymmetric. Supervenience claims do not, in general, entail “in virtue of ” claims.

Every property supervenes on its complement, but of course nothing has a property F in virtue of having its complement not-F because nothing has both F and not F (at least at the same time). Further, properties that everything necessarily has, and ones that nothing could possibly have, supervene on any property whatsoever.

Ontological priority

The necessary property being an electron or not an electron trivially supervenes on the property being an antique; and the necessarily uninstantiated property being an electron and not being an electron does well.

The reason is that no two things can differ with respect to either such noncontingent property; and so, trivially, for any property, no two things can differ with respect to them without differing with respect to it. But there is no ontological priority in such cases.

6. Superduper venience

Supervenience is just the relation of functional dependence: A-properties supervene on B-properties just in case how something is with respect to A-properties is a function of how it is with respect to B-properties. Given that, when A-properties supervene on B-properties, we expect there to be some explanation of why that is so.

Superduper venience

In the case of logical supervenience, the explanation might be that Aproperties are necessary properties or that they are properties nothing could have. Or the explanation might be that A-properties are identical with B properties.

Or the explanation might be that A-properties are determinables of B-properties and B-properties are all the determinates of A-properties, as being colored is a determinable of all the shades of color (being red, and so on), and they are determinates of being colored.

And in the case of merely nomological supervenience, the explanation will appeal to a law of nature. (This list of possible explanations is not intended to be exhaustive.)

law of nature

When a supervenience relation is explainable, there is “superdupervenience”. Appeals to in principle unexplainable supervenience—supervenience without the possibility of superdupervience—would arguably be mystery-mongering.

7. supervenience, conceptual analysis, and reduction

Although logical supervenience does not suffice for conceptual analysis, the latter requires the former: if A-factors can be conceptually analyzed in terms of B-factors, then A-factors logically supervene on B-factors. Supervenience is thus useful in testing claims that a certain a kind of conceptual analysis is possible.

According to a simple causal theory of perceptual knowledge, a subject’s perceptual knowledge that P can be analyzed as P’s bearing an appropriate causal connection to the subject’s perceptual belief that P. To test the claim, one need not await a specific proposal as to what kind of causal connection is appropriate.

supervenience, conceptual analysis, and reduction

For such a conceptual analysis is possible only if two believers that P cannot differ with respect to perceptually knowing that P without differing with respect to how the fact that P is causally connected to their belief that P.

This supervenience thesis is open to refutation by a single counterexample. The well-known “fake barn country” case yields a putative counterexample to this thesis.

Thus, the claim that a certain kind of conceptual analysis is possible can be refuted by appeal to a false implied supervenience thesis (or, FIST). Claims that certain kinds of reductions are possible can be similarly tested by their implied supervenience theses.

8. Individual/global supervenience

Individual/global supervenience

There is a distinction between individual supervenience and global supervenience. The former concerns differences in individuals; the latter concern differences in possible worlds.

The claim that individuals cannot differ with respect to their moral properties without differing with respect to their natural properties is an individual supervenience thesis.

The claim that possible worlds cannot differ with respect to what general truth hold in them without differing with respect to what particular truths hold in them is a global supervenience thesis.

9. Strong/weak individual supervenience

Strong/weak individual supervenience

Two nonequivalent kinds of individual supervenience have been formulated as follows:

POSSIBLE-WORLDS WEAK INDIVIDUAL SUPERVENIENCE. A-properties weakly supervene on B-properties if and only if in any possible world w, B-indiscernible individuals in w are A-indiscernible in w.

POSSIBLE-WORLD STRONG INDIVIDUAL SUPERVENIENCE. A-properties strongly supervene on B-proper- ties if and only if for any possible worlds w and w* , and any individuals x and y,if x in w is B-indiscernible from y in w* , then x in w is A-indiscernible from y in w* .

logically possible

The possible worlds quantified over might be all logically possible worlds or only all nomologically possible worlds (and so on); thus, weak and strong supervenience relations can have different modal strengths. As the names suggest, strong supervenience is stronger than weak supervenience (modulo sameness of modality).

When the range of worlds is the same, strong supervenience of A-properties on B-properties entails weak supervenience of A-properties on B-properties, but the latter does not in general entail the former.

Notions of weak and strong individual supervenience have also been formulated as follows, using the modal operator necessarily rather than quantification over possible worlds.

weakly supervene

OPERATOR-WEAK INDIVIDUAL SUPERVENIENCE. A-properties weakly supervene on B-properties if and only if necessarily, for any A-property F, if something has F, then there is a B-property G such that it has G, and whatever has G has F.

OPERATOR-STRONG INDIVIDUAL SUPERVENIENCE. A-properties strongly supervene on B-properties if and only if necessarily, for any A-property F, if something has F, then there is a B-property G such that it has G, and necessarily whatever has G has F.

The strong version is formulated exactly like the weak version except that it contains one more necessity operator. The two modal operators in the strong case can be the same or different.When all of the modal operators are the same, strong supervenience entails weak supervenience, but the latter does not in general entail the former.

10. Supervenience and internalism/externalism distinctions

Supervenience and internalism/externalism distinctions

Individual supervenience has proved useful for formulating various kinds of internalism/externalism distinctions. For example, according to internalists about mental content, what content a mental state has will strongly supervene on intrinsic properties of the subject of the mental state.

Content externalists deny such supervenience, and indeed typically deny there is even weak supervenience: they typically hold that two subjects within a possible world can be intrinsic duplicates while being in mental states with different contents. (Twin-Earth cases [Putnam 1975] are invoked in would-be arguments by appeal to FISTs against internalist theories of content.)

Similarly, an internalist about epistemic justification asserts that whether a belief is justified strongly supervenes on what mental states the subject is in. Epistemic externalists deny that, and indeed deny that whether a belief is epistemically justified even weakly supervenes on what mental states the subject is in.

Epistemic externalists

Moreover, supervenience has been employed to capture the traditional distinction between internal and external relations (Lewis 1986a): internal relations (such as being taller than) strongly supervene on the intrinsic natures of its relata, whereas external relations (such as being three kilometers from) fail to even weakly supervene on the intrinsic natures of its relata.

11. Weak supervenience without strong supervenience

There can be weak supervenience without strong supervenience. But when this is the case, we expect an explanation of why weak supervenience holds that does not entail that strong supervenience holds as well.

In any possible world, if two individuals assert exactly the same propositions, then they are exactly alike in having asserted a true proposition: The one will have asserted a true proposition if and only if the other did. The explanation is that any proposition will have a unique truth value relative to a world.

Weak supervenience without strong supervenience

But since contingent propositions are true in some worlds but not in others, strong supervenience fails in the case in question. It has been claimed that, although moral properties weakly supervene on natural properties, they do not strongly supervene on them.

And it has been claimed that, although mental properties weakly supervene on physical properties, they do not strong supervene on them. Defense of these claims requires an explanation of why weak supervenience holds despite the failure of strong supervenience.

Although attempts have been made to provide such an explanation in the moral case, there has been no attempt in the mental case. Many philosophers doubt such an explanation is possible in the mental case.

12. Global supervenience

Global supervenience

Global supervenience has been invoked in the formulation of various philosophical doctrines. David Lewis’s (1986a, x) doctrine of Humean Supervenience, according to which everything supervenes on the pattern of perfectly natural qualitative properties across spacetimes points, is a global supervenience thesis.

Although Donald Davidson proposed a weak individual supervenience thesis to characterize the dependency of mental properties on physical properties, several attempts have been made to characterize physicalism as a global supervenience thesis.

For example, Frank Jackson has proposed the following formulation: Any possible world that is a minimal physical duplicate of our world is a duplicate simpliciter of it.

Frank Jackson

A physical duplicate of our world is any world exactly like it in every physical respect—with respect to its worldwide pattern of distribution of physical properties and relations, its physical laws, and so on. A minimal physical duplicate is any physical duplicate that contains nothing other than what is metaphysically necessary to be a physical duplicate.

It is controversial whether this thesis suffices for physicalism; unlike physicalism, it seems compatible with the existence of a necessarily existing God. But even if it does not suffice, if physicalism requires it, then it earns its keep.

A substantive condition of adequacy on physicalism would be that it explain why the supervenience thesis is true. And physicalism itself would rendered testable, even in the absence of a fully adequate formulation.

phenomenally conscious

Given that we are phenomenally conscious, if, as some philosophers maintain, a “zombie world” is possible—a world that is a minimal physical duplicate of our world but entirely devoid of phenomenal consciousness—then physicalism is false. Of course, the success of this would be refutation by appeal to a FIST turns on the controversial issue of whether a zombie world is indeed possible.

13. Weak, intermediate, and strong global supervenience

A variety of different kinds of global supervenience has been formulated:

A-properties weakly globally supervene on B-properties if and only if, for any worlds w1 and w2, if there is a B-preserving isomorphism between w1 and w2, then there is an A-preserving isomorphism between them.

Weak, intermediate, and strong global supervenience

A-properties intermediately globally supervene on B-properties if and only if, for any worlds w1 and w2, if there is a B-preserving isomorphism between w1 and w2, then there is at least one isomorphism between them that is both A-and-B-preserving (Shagrir 2002, Bennett 2004).

A-properties strongly globally supervene on B-properties if and only if, for any worlds w1 and w2, every B-preserving isomorphism between w1 and w2 is an A-preserving isomorphism between them. (McLaughlin 1996, 1997; Stalnaker 1996; Sider 1999).

Strong global supervenience entails intermediate global supervenience, which entails weak global supervenience. But the converse entailments all fail to hold in general.

14. Some equivalancies

Some equivalancies

The plethora of technical definitions of kinds of supervenience gives the appearance of more variety than there is. Strong individual supervenience entails strong global supervenience (Kim 1984), but strong global supervenience does not in general entail strong individual supervenience (Paull and Sider 1992).

Nevertheless, strong individual supervenience and strong global supervenience are equivalent in cases in which the base set of properties B is closed under Boolean operations and ones involving quantification and identity (Stalnaker 1996).

Strong individual supervenience is also equivalent to strong global supervenience in cases in which A and B are sets of intrinsic properties (Shagrir 2002, Bennett 2004).

Donald Davidson

It has, moreover, been compellingly argued that in cases in which A and B are sets of intrinsic properties, weak and strong individual supervenience are equivalent as well. Weak individual supervenience, strong individual supervenience, and strong global supervenience are equivalent for sets of intrinsic properties.