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Initially, some philosophers such as G. E. Moore and R.M. Hare firstly introduces the idea of supervenience in ethics. Later, the idea of supervenience is also used in the philosophy of mind, and Donald Davison is perhaps the first philosopher who introduces supervenience into the discussion of the mind-body problem. In ethics, philosophers discuss whether ethical properties supervene on non-ethical properties. In philosophy of mind, philosophers discuss whether mental properties supervene on physical properties. Also, philosophers discuss whether the idea of supervenience can be an alternative version of physicalism from reductive physicalism1. Although supervenience is closely related to ethics and the philosophy of mind, it can also be a philosophical topic itself. As an introductory paper of supervenience, I am not going to put my effort discussing the specific role of supervenience in ethics or in the philosophy of mind. Instead, I will discuss and explain the general idea of supervenience in detail. A general idea is that supervenience is a relation of dependency between two kinds 1 Briefly, physicalism is the view that the real world is nothing more the physical world. Physicalism in the philosophy of mind is the view that mental events or states are not independent from physical things. Reductive physicalism in the philosophy of mind even holds that mental events or states can be reductively explained by terms in physics and laws in physics. In contrast, non-reductive physicalists think that mental events or states cannot be reductively explained by terms or laws in physics, even though mental events and states are still physical things. It is an open discussion whether supervenience can be used in non-reductive physicalism. That is, it is still not clear whether mental properties can supervene on physical properties without reductive explanation. of properties. The basic idea of dependency is that if A-properties depend on B-properties, then B-properties determine A-properties. If B-properties determine A-properties, then it is not possible that B-properties are fixed while A-properties can still vary. In other words, there is a covariant relationship between A-properties and B-properties. This means that if two possible situations are indiscernible with respect to B-properties, they are also indiscernible with respect to A-properties. Thus, the intuitive idea of supervenience is that if A-properties supervene on B-properties, then if two possible situations are indiscernible with respect to B-properties, they are also indiscernible with respect to A-properties. There are different versions of supervenience when we analyze the intuitive idea of supervenience in depth. Kim (1993, 1994) divides supervenience into three versions, namely weak supervenience, strong supervenience, and global supervenience. Weak supervenience means that if A-properties weakly supervene on B-properties, then if in any logically possible world, two individuals, x and y, are indiscernible with respect to B-properties, then x and y are also indiscernible with respect to A-properties. Strong supervenience says that no matter individuals x and y are in the same logically possible world or in different logically possible worlds, if x and y are indiscernible with respect to B-properties, x and y are also indiscernible with respect to A-properties. Global supervenience means that if two worlds are indiscernible with respect to B-properties, these two worlds also are indiscernible with respect to A-properties. These versions of supervenience have complicated relationships. First of all, the difference between weak supervenience and strong supervenience depends on the notion of logical possibility. In the broadest sense, a logically possible world is any world that we can conceive of. As Chalmers (1996) writes, “one can think of it loosely as possibility in the broadest sense, corresponding roughly to conceivability, quite unconstrained by the laws of our world” (p.35). Being conceivable means we can imagine anything without violating any logic rule. To illustrate, we can imagine a world without gravity, or we can imagine a world with many flying unicorns. They are conceptually coherent, even though there is gravity and no flying unicorn in our world. In contrast, we cannot imagine a world where exists a triangle with four angles. We cannot imagine such a world because “a triangle with four angles” is a necessarily false statement. That is, the statement is logically impossible to be true. Although the detail of logically possible worlds is quite controversial, the above information should be enough to explain the broadest meaning of logically possible worlds. The understanding towards this broadest meaning of logically possible worlds enables us to explain the difference between weak supervenience and strong supervenience. If A-properties weakly supervene on B-properties, then A-properties only supervene on B-properties within a logically possible world. Thus, if an individual x is in a logically possible world, and y is in another logically possible world, then x and y may have indiscernible B-properties but discernible A-properties. In other words, unless x and y are in the same world, their supervenient relationship may not hold. In contrast, if A-properties strongly supervene on B-properties, then A-properties supervene on B-properties not only within a logically possible world, but also in different logically possible worlds. Thus, no matter x and y are in the same world or in different worlds, x and y cannot be discernible with respect to A-properties if they are indiscernible with respect to B-properties. Weak supervenience is only an intra-world relationship; while strong supervenience is both an intra-world and a cross-world relationship. Therefore, it is clear that strong supervenience entails weak supervenience, but weak supervenience does not entail strong supervenience. Global supervenience differs with weak supervenience or strong supervenience in terms of that the “unit” of global supervenience is a world, but not an individual. It is not hard to see that weak supervenience does not entail global supervenience. This is because weak supervenience only tells us the relationship between two individuals within the same world, but it does not tell us the relationship between two properties of two worlds. It is also easy to see that strong supervenience entails global supervenience because strong supervenience includes a cross-world relationship. Does global supervenience entail strong supervenience or weak supervenience? It is a controversial question, and different philosophers have different answers to this question. For instance, Chalmers (1996) believes that supervenience in terms of worlds does not entail supervenience in terms of individuals. An example of his idea is that biological properties supervene globally on physical properties, but biological properties do not supervene individually on physical properties. He writes, “Two physically identical organisms can arguably differ in certain biological characteristics. One might be fitter than the other, for example, due to differences in their environmental contexts” (p.34). So, according to Chalmers, global supervenience does not entail either strong supervenience or weak supervenience. Different from Chalmers, Kim (1993) has different ideas in different periods about whether global supervenience entails strong supervenience or weak supervenience. Initially, he thinks that global supervenience is equal to strong supervenience; therefore global supervenience entails both strong supervenience and weak supervenience2 (Kim, 1993, p.69). However, later he finds a counterexample which shows that global supervenience does not entail strong supervenience (p.82-83). Finally, he gives up that counterexample and concludes that “the question of the relationship between global and strong supervenience has not been fully settled” (p.170)3. From the ideas of 2 Global supervenience entails strong supervenience because they are equivalent. Global supervenience entails weak supervenience because strong supervenience entails weak supervenience, and global supervenience is equal to strong supervenience. 3 Although the references in this paragraph are from the same book, there are actually three different papers from different years. These three papers are: “Concepts of Supervenience”, which is originally Chalmers and Kim, we find that different philosophers have different ideas on the entailment relationship between global supervenience and strong or weak supervenience, and there is no unique answer for the issue. In a word, it is more objective to conclude that although supervenience is a widely used idea in ethics and in the philosophy of mind, the detail of supervenience is still Bibliography
Blackburn, S. (1998). “Supervenience”. In Craig, E. (ed.), Routledge Encyclopedia of Philosophy. Routledge, Vol. . London. pp. 235-238. Chalmers, D. (1996) The Conscious Mind. Oxford University Press. U.S.A. Kim, J. (1993). Supervenience and Mind. Cambridge University Press. U.S.A. Kim. J. (1994). “Supervenience”. In Guttenplan, S. (ed.), A Companion to the Philosophy of Mind. Blackwell Publishers. UK. pp. 575-583 Loewer, B. (1998). “Supervenience of the Mental” in Craig, E. (ed.), Routledge Encyclopedia of Philosophy. Routledge, Vol. . London. pp. 238-240. printed in 1984; “‘Stong’ and ‘Global’ Supervenience Revisited”, which is originally printed in 1987; and the last one is “Postscripts on Supervenience”, which is a newly published article in his book (Kim, 1993).

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