Hong Kong Society of Humanistic Philosophyˇ@ http://www.arts.cuhk.edu.hk/~hkshp An introduction to supervenience Benedict Chanˇ]M. Phil. Student, Phil. Dept., H.K.U.ˇ^ Initially, the idea of supervenience is firstly introduced in ethics by some philosophers, such as G. E. Moore and R.M. Hare. 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 also discuss whether the idea of supervenience can be an alternative version of physicalism from reductive physcialism[1]. Although supervenience is closely related to ethics and 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 to discuss the role of supervenience in ethics or in philosophy of mind. Instead, I will discuss and explain the idea of supervenience in detail. A general idea is that supervenience is the relation of dependency between two kinds of properties. It may always be an open discussion of what dependency is. However, the intuitive idea of dependency is that if A-properties are dependent 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 deeply. "Two situations" in the intuitive idea of supervenience can be treated as two individuals or two worlds. Kim (1993, 1994) divides supervenience into three versions, namely weak supervenience, strong supervenience, and global supervenience. Weak supervenience and strong supervenience are in terms of individuals, while global supervenience is in terms of worlds. 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 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 indiscernible with respect to A-properties. The relationships between these versions of supervenience are complicated. 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). Conceivability means that anything we can imagine without to violate 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 our world has gravity, and our world does not have any flying unicorn. In contrast, we cannot imagine a world which has a triangle with four angles. We cannot imagine such a world because "a triangle with four angles" is a necessary 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 sufficient to explain the broadest meaning of logically possible worlds. Once we understand this broadest meaning of logically possible worlds, it is enough for us to explain the difference between weak supervenience and strong supervenience. The difference is like this. 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 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, and 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, he should think that global supervenience does not entail both strong supervenience and 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, and so global supervenience entails both strong supervenience and weak supervenience[2] (Kim, 1993, p.69). However, later he finds a counterexample which shows that global supervenience does not entail strong supervenience (p.82-83). But finally, he gives up that counterexample and concludes that "the question of the relationship between global and strong supervenience [thus also weak supervenience] has not been fully settled" (p.170)[3]. From the ideas of 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 a unique answer for the issue. In conclusion, it is safe to conclude that although supervenience is a widely used idea in ethics and in the philosophy of mind, the detail of supervenience is still under development and discussion. 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. [1] Briefly, physicalism is the view that the real world is nothing more the physical world. Physcialism 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 or laws in physics. In contrast, non-reductive physcialists 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 physcialism. That is, whether mental properties supervene on physical properties without reductive explanation. [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, they are actually belonged to three different papers in different periods. These three papers are: "Concepts of Supervenience", which is originally printed in 1984; "'Stong' and 'Global' Supervenience Revisited", which is originally printed in 1987; the last one is "Postscripts on Supervenience", which is a newly published article in his book (Kim, 1993). Copyright (c) Hong Kong Society of Humanistic Philosophy. All Rights Reserved.