STEPHEN P. SCHWARTZ
KINDS, GENERAL TERMS, AND RIGIDITY: A REPLY TO LAPORTE (Received 4 October 2001; received in revise...
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STEPHEN P. SCHWARTZ
KINDS, GENERAL TERMS, AND RIGIDITY: A REPLY TO LAPORTE (Received 4 October 2001; received in revised version 30 April 2002) ABSTRACT. Joseph LaPorte in an article on ‘Kind and Rigidity’ (Philosophical Studies, Volume 97) resurrects an old solution to the problem of how to understand the rigidity of kind terms and other general terms. Despite LaPorte’s arguments to the contrary, his solution trivializes the notion of rigidity when applied to general terms. His arguments do lead to an important insight however. The notions of rigidity and non-rigidity do not usefully apply at all to kind or other general terms. Extending the notion of rigidity from singular terms such as proper names to general terms such as natural kind terms is a mistake.
I
The formal semantics of rigidity for singular terms is straightforward. A rigid singular term, such as a proper name, designates the same individual in every possible world in which that individual exists. Kripke (1980) and Putnam (1975) boldly extended the notion of rigidity to general terms and especially natural kind terms. In the case of general terms, however, the formal semantics of rigid designation has never been clarified. The informal idea of rigidity is that the reference or designation must stay the same in every relevant possible world. With general terms there is no obvious candidate for what is to stay the same. With singular terms the individual named is the extension of the term – it is the term’s reference or designation. It stays the same if the term is rigid. But the extension of a general term will vary from world to world – the set of tigers in some other possible world need not contain the same individuals as the set of actual tigers. This is especially disappointing because if rigidity of natural kind terms is to be understood on analogy with that of proper names, we would expect the extension of a rigid term to remain the same from world to world. That it typically does not means that the Philosophical Studies 109: 265–277, 2002. © 2002 Kluwer Academic Publishers. Printed in the Netherlands.
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analogy between rigid singular terms and rigid general terms cannot be as neat as we would like. Early in the discussion of rigidity several philosophers suggested that a rigid general term be understood to rigidly designate a kind or sort.1 At first blush this seems like a useful suggestion since natural kind terms such as ‘gold’, ‘water’, and ‘tiger’ will clearly come out rigid. Each will designate the same kind as it does in the actual world in every possible world in which it designates at all. Alas, as several authors pointed out this solution is unsatisfactory because, among other things, it extends the privilege of rigidity to just about all general terms (Schwartz, 1980). ‘Bachelor’ will designate the same kind – the same marital status – in every possible world in which it designates. Likewise for other nominal kind terms. They all turn out to be rigid. To some this result would be welcome, but it seems to me to lose all the ground gained. Rigidity has lost its exclusivity, like a club of which all are automatically members, and thereby its interest. Clearly there is an important difference between natural kind terms like ‘gold’ and nominal kind terms like ‘bachelor’ – and isn’t this difference based on the rigidity of the one and nonrigidity of the other? Since the proposed solution lost this difference it was abandoned. The basic problem is that this proposed solution trivializes rigidity.
II
Recently in this journal Joseph LaPorte (2000) has argued in favor of this easy solution. In particular he has argued that the fact that nominal kind terms as well as natural kind terms come out rigid is no reason to abandon the proposed solution (i.e. that rigid general terms are rigid in virtue of designating the same kind in every world in which they designate). In my view, LaPorte’s attempt to resurrect this account – that he calls ‘his preferred account’ – fails, but he has sharpened the discussion significantly and importantly and perhaps paved the way for a correct solution, so I think it is worth carefully going over this ground once again. LaPorte is ready to embrace the fact that under his preferred account terms like ‘bachelor’ and ‘hunter’ come out rigid. Thus the rigid/non-rigid distinction does not reflect the natural kind/artificial
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kind distinction for LaPorte (299). He claims that this does not trivialize rigidity because not all general terms will be rigid. LaPorte’s interesting example relies on the humble honeybee. The term ‘honeybee’ is a natural kind term that picks out the kind honeybee rigidly – it designates the same kind in every possible world according to LaPorte. On the other hand ‘the insect species that is typically farmed for honey’ designates the honeybee in the actual world but in other possible worlds it will designate different kinds. Thus according to LaPorte in this way we have a viable distinction between rigid and non-rigid general terms. “The rigidity of ‘the honeybee’ would seem, then, to find a contrast in certain descriptions, just as the rigidity of names such as ‘Hesperus’ and ‘Ben Franklin’ do” (p. 297). Furthermore this distinction “. . . is significant because it is necessary to distinguish these types of expressions for the purpose of determining whether certain statements are necessarily true. The differences between these two types of expressions for kinds are significant for the very reasons that the differences between expressions like ‘Ben Franklin’ and ‘the inventor of bifocals’ are significant” (p. 297). Just as e.g. ‘Hesperus = Phosphorus’ is necessarily true so is ‘The honeybee = Apis mellifera’. On the other hand ‘The honeybee = the insect species that is typically farmed for honey’ is contingently true, just as is ‘Ben Franklin = the inventor of bifocals’ and ‘Hesperus = the brightest celestial object, apart from the moon, in the evening sky’. According to LaPorte this shows that there is a “. . . parallel between ‘the honeybee’ and ‘Hesperus’, on the one hand, and ‘the insect species that is typically farmed for honey’ and ‘the brightest celestial object, apart from the moon, in the evening sky’ on the other . . .” (p. 298). Below I will argue in detail that this supposed parallel is in fact spurious, but first we must peer into the metaphysical realm where the deep issues lie.
III
Unfortunately LaPorte is only able to float his preferred solution on some dubious metaphysical claims. LaPorte’s claim that ‘the insect species that is typically farmed for honey’ picks out different species in different worlds whereas ‘the honeybee’ picks out the same
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species in every world is based on his position that the honeybee is a genuine kind whereas the insect species that is typically farmed for honey is not. LaPorte recognizes that his preferred account will be trivialized if we allow what he calls the abstruse kind insect species that is typically farmed for honey. Consequently he denies that there are such kinds. He concludes that “. . . my division of kind designators into a rigid and a non-rigid camp is not threatened by metaphysical troubles concerning unusual kinds” (p. 302). I do not believe however that LaPorte’s rejection of what he calls abstruse kinds will help his preferred account avoid the triviality charge. His talk of kinds, regular or abstruse, is really a dodge that hides the central metaphysical issue. In a footnote LaPorte says: Just what sort of abstract entity might be designated by a natural kind term is a matter of dispute, one that for the purposes at hand does not require a resolution: besides the view that ‘whale’ names the whale kind . . . there is the position that it is the property or attribute whales have in virtue of being whales that is designated. I will speak, for simplicity, of the designated entity as a kind (p. 311).
The problem with LaPorte’s position is that, as standardly understood, in possible worlds there aren’t any kinds at all, regular or abstruse – kinds may have an important role in our common sense understanding of the world and even in science but they don’t have a metaphysical status that is useful to formal semantics2 – nor would his position be helped by talk of properties. Indeed, its difficulties come out more clearly if we focus on properties. Possible worlds, as standardly conceived by metaphysicians, consist of individuals and properties, and properties are just sets of individuals, actual and possible. There isn’t anything else (see Plantinga, 1977, especially ‘The Canonical Conception of Possible Worlds’, 254–255, and Lewis, 1986). Furthermore, there are lots and lots of properties. Again, as standardly understood there is a property for just about every possible description and every boolean function of descriptions, and there are still a lot more. When considering possible worlds, properties are not limited to robust things like causal powers – they are simply sets of actual and possible individuals and for every such set there is a property. I say there is possible world in which snow is the same color as my car. What does this mean? That there is a possible world in which snow has the property of being the same color as my car.
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‘Being a honeybee’ names a property, so does ‘being an insect of the species typically farmed for honey’ (in this case a complex relational property) and so does ‘being the inventor of bifocals’. And it follows in the standard conception that when talking about other possible worlds these name the same properties as they do when talking about the actual world. The color of my car is different in different possible worlds but the property ‘being the same color as my car’ is the same relational property in every possible world. At least this is how properties are usually understood in talk of possible worlds (Lewis, 1986, especially ‘Modal Realism at Work: Properties’, 50–69). Perhaps, however, we do not want to follow such committed metaphysicians as Lewis and Plantinga in allowing so many properties. Perhaps we want to take a more scientific approach and only allow properties recognized by some version of advanced science. To make this approach useful LaPorte would have to restrict properties to ‘natural properties’ or ‘scientifically recognized properties’ or something similar.3 The following might be promising: ‘honeybee’ designates the same natural property in every possible world and so does e.g. ‘red’ but ‘the insect species that is typically farmed for honey’ and ‘being the same color as my car’ do not. After all in some worlds my car is red in others green. Now however we have the problem of figuring out what properties are natural and when they are identical and so on. Does ‘being a bachelor’ designate the same natural property in every possible world (and thus come out rigid according this proposal)? ‘Bachelor’ denotes the same marital status from world to world, as we know – so the answer seems to be ‘yes’. But marital customs may vary from world to world in subtle and not so subtle ways. So is it the exact same marital status if the marital customs vary? How much do they have to vary before it is different? Is ‘being a bachelor’ a natural property? Is it or would it be a scientifically recognized property? I do not think that there are any easy answers to these questions (nor does Lewis, 1986). The difficulty for LaPorte really comes down to the fact that no one is sure what kinds and properties really are, how many there are, and how to identify them. With singular terms rigidly designating individual physical objects we do not have these serious problems. Even though there are philosophical difficulties about personal iden-
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tity, there is an object that we can see and touch that is e.g. a person, and thus rigidly name. In the case of kind and property terms there is no common sense uncontroversial abstract object to refer to. We can make one up or stipulate one, but LaPorte has not made clear how these metaphysical stipulations have anything to do the functioning of natural kind terms in natural language.
IV
As promised let us now consider the analogy that LaPorte sees between ‘Hesperus = Phosphorus’ and ‘The honeybee = Apis mellifera’. Just as e.g. ‘Hesperus = Phosphorus’ is necessarily true so is ‘The honeybee = Apis mellifera’. LaPorte claims that recognizing the rigidity of the terms ‘the honeybee’ and ‘Apis mellifera’ is needed to explain the necessity of ‘The honeybee = Apis mellifera’. This is the main work that the rigidity of a general term is supposed to do. The difficulty for LaPorte is that the analogy is spurious. ‘Hesperus = Phosphorus’ is necessarily true, and that in itself is pretty surprising, but also we must remember that it is a posteriori and not analytic – not true by definition. That Hesperus = Phosphorus was a discovery and an unanticipated one at the time. Announcing that these sorts of identities are necessarily true (if true at all) and a posteriori and thus not analytic was a remarkable advance in semantics and made Saul Kripke justly famous. Now consider ‘The honeybee = Apis mellifera’. In order for LaPorte’s point to be effective this claim must be not only necessarily true but a posteriori – a discovery. But I cannot see that it is. Did biologists discover that the honeybee is Apis mellifera as astronomers discovered that Hesperus is Phosphorus? Did we need Kripke to tell us that ‘The honeybee = Apis mellifera’ is necessarily true? Could we (epistemically) discover that it turns out that the honeybee is not Apis mellifera?4 Since the answer to these questions is at least arguably ‘No’, there seems to be no clear parallel between ‘Hesperus = Phosphorus’ and ‘The honeybee = Apis mellifera’. Nor does ‘The honeybee = Apis mellifera’ seem to be like ‘Water = H2 O’. ‘Water = H2 O’ is necessarily true and a posteriori in the way that ‘Hesperus = Phosphorus’ is, but it is giving the essence or
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underlying trait of water, its chemical composition. ‘The honeybee = Apis mellifera’ is not giving the biological essence or underlying trait of the honeybee – that would have to be something about its DNA presumably. So ‘The honeybee = Apis mellifera’ is not analogous to ‘Water = H2 O’ either. They are different types of necessarily true statements. I would say that the truth of ‘The honeybee = Apis mellifera’ is based more on decision than a discovery and thus that the statement is rather analytic in nature. Thus it seems that LaPorte’s proposal to treat rigid general terms as rigidly designating their kinds is not needed to explain the necessity of ‘The honeybee = Apis mellifera’. Even more controversially, LaPorte wants to condone extending rigidity to terms like ‘bachelor’ and ‘hunter’. Likewise LaPorte contends that such terms as ‘soda’, ‘soda pop’, and ‘pop’ are rigid, and that the relevant features of necessity carry over: The connection to necessity is straightforward. ‘Soda = the beverage my uncle requests at Super Bowl parties’ is true but not necessarily true, since the second designator is not rigid; it refers to milk, or juice in some worlds, and in those worlds, the sentence is false. ‘Soda = pop’ is, on the other hand, necessarily true, since it is true and both designators rigidly designate soda pop. (p. 299)
But again we do not need the semantics of rigidity to explain the necessity of ‘soda = pop’ or ‘bachelors are unmarried males’ or ‘hunters are people who hunt’. These types of statements were well known to be necessary on the basis of meanings long before Saul Kripke was born. Furthermore, the supposed rigidity of terms like ‘hunter’, ‘bachelor’, and ‘soda’ does not support necessarily true but a posteriori identities like ‘Hesperus = Phosphorus’ or ‘water = H2 O’. If there are no necessary a posteriori propositions with ‘bachelor’, ‘hunter’, ‘soda’, then their supposed rigidity offers nothing new or interesting at all and extending rigidity to them illuminates nothing. The fact that LaPorte does not offer any candidates for necessarily true but a posteriori identities with terms like ‘soda’, ‘bachelor’, or ‘hunter’ – and none spring to mind – strongly suggests that LaPorte’s preferred account is no solution at all – even if he could solve his problems about abstract objects. In other words, his proposal to understand the rigidity of general terms as designating the same kind in every possible world does trivialize rigidity. It does
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not help us to understand the striking and interesting distinction between terms such as ‘gold’ on the one hand and ‘bachelor’ on the other; nor does it offer any new insight into the source of necessary statements using ‘bachelors’ and other similar terms. My view is that LaPorte’s understanding of rigidity of general terms merely reflects the obvious and rather uninteresting fact that words have the same meaning when talking about other possible worlds as they do when talking about the actual world. That LaPorte is confusing rigidity with consistency of meaning is indicated by the following passage: Some names (‘water’ for example . . .) might pick out the same substance in every possible. These would rigidly refer to a substance. . . . But other names might rigidly refer to chemical composition (say H2 O), even if they do not rigidly refer to a substance. . . . Others might rigidly refer to a species, an occupation, a marital status, and so on. In each case, the objects that instantiate the kind vary from world to world. But the kind itself is the same, from world to world. (p. 306)
This is just consistency of meaning when talking about other possible worlds, but dressed up in fancy clothing. If I say ‘there is a possible world in which Bill Clinton was removed from office’ what I say is true and means there is a possible world in which Bill Clinton was removed from office. Not only does Bill Clinton designate the same individual in that possible world as in the actual world, but ‘removed’ is the same action, ‘office’ means office, and so on. There is nothing surprising about this, and it does not shed any light on the nature of necessity, or the formal semantics of singular or general terms. That words have the same meaning when talking about other possible worlds as they do when talking about the actual world is not the same as the interesting fact that some singular terms, notably proper names, have the same designation (i.e. extension) in all possible worlds whereas definite descriptions typically designate different individuals in different worlds. ‘The inventor of bifocals’ means the inventor of bifocals when we use it to talk about other possible worlds – but it designates different individuals in different worlds. Confusing rigidity with consistency of meaning, as LaPorte apparently does, is no advance in semantics. Here then is the challenge: Explain what it means for e.g. ‘gold’, ‘tiger’, ‘water’ to be rigid just using set theoretic tools and possible worlds made up of individuals actual and possible (and perhaps
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using the notion of natural property). We can do it easily for rigid singular terms. A proper name that is rigid is a constant function from possible worlds to individuals. I.e. it takes the same individual at every possible world in which it designates at all. The corresponding try with general terms does not work. A rigid general term is not a constant function from possible worlds to sets of individuals. Nor will talk of natural properties help us. Of course, a rigid general term names the same property in every possible world because trivially words keep the same meanings when talking about other possible worlds. This will be the case with virtually all general terms, even the ones that LaPorte wants to come out non-rigid. LaPorte’s preferred account does not meet the challenge.
V
LaPorte does, however, point the way to what I think is the correct account. He insists that there is an obvious distinction between natural kind terms like ‘whale’ on the one hand and nominal kind terms like ‘bachelor’ on the other – only that this difference is not explained by rigidity. “It is the causal theory that explains how a term like ‘whale’ is different from a term like ‘bachelor’ ” (p. 304). The idea is that natural kind terms somehow get their references fixed by causal relations whereas nominal kind terms do not, and this is enough to explain the difference between the two kinds of terms. LaPorte also points out that rigidity is not the same as indexicality. Indeed there are a number of things that need to be distinguished (and were not carefully distinguished in early discussions of these issues). Among the things that need to be distinguished are rigidity, indexicality, non-descriptionality, getting reference by causal chains, having its essence discovered empirically, and perhaps there are others (see e.g. Abbott, 1979; Burge, 1979, 1996). None of these seem to imply the others. LaPorte has got it right. The notion of rigidity does no work in explaining the difference between natural kind terms and nominal kind terms. But I urge that we go further and acknowledge that the notion of rigidity does no work at all when applied to general terms. As I have argued above, contrary to LaPorte, it sheds no new light on necessary truths involving nominal kind terms, and
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those necessary a posteriori truths involving natural kind terms can be explained by other features. (See Salmon (1981) for extensive discussion of these issues.) Although I cannot provide a full account here I do not think that rigidity will help explain the necessity of these a posteriori truths because many necessary a posteriori truths are not identities. For example, ‘water is a compound’, ‘gold is an element’, and ‘tigers are animals’ are necessarily true (if true) and a posteriori. So the necessity of identities between rigid designators will not explain the necessity of these claims, since they are not identities. Note that we do not even know of any non-trivial true identities in many cases, e.g. tiger, and yet we do know a posteriori that e.g. necessarily tigers are animals. We should expect that the account that explains why ‘Water is a compound’ is a necessary a posteriori truth will also explain why ‘Water = H2 O’ is necessarily true if true and a posteriori. The necessity of identities between rigid designators cannot be that account. (On this see Donnellan, pp. 92–93.) Devitt and Sterelny, recognizing some of these problems with rigid designation, have suggested replacing the notion that natural kind terms are rigid designators with the idea that they are ‘rigid appliers’. Let us say that for a general term ‘F’ to be a rigid applier is for it to be such that if it applies to an object in the actual world, and that object exists in another possible world, then it applies to that object in that world. . . . The problem then [with traditional description theories] seems to be that natural kind terms are rigid appliers whereas the descriptions alleged to be synonymous with them are not. (Devitt and Sterelny, p. 85)
This may be a useful suggestion because rigid application would do much of the work we would expect from rigid designation. It helps to refute the traditional description theory, it enables us to distinguish semantically between e.g. ‘bachelor’ and ‘gold’, and it does a nice job of explaining the necessity of e.g. ‘All tigers are animals’, since both ‘tiger’ and ‘animal’ are rigid appliers. The notion of rigid application is not, however, without problems of its own. For example, not all natural kind terms are rigid appliers. For example, many stage terms and gender terms would not be rigid appliers. Consider the natural kind term ‘frog’. Since tadpoles turn into frogs there will be frogs in the actual world that never get to be
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frogs in some other possible world, because they never get past the tadpole stage in that world. ‘Frog’ then is not a rigid applier. Likewise for any natural kind terms that allow for change from one to the other as perhaps ‘man’ and ‘woman’ do. Change in the actual world does not entail similar change in every possible world. Thus rigid appliers would only apply to natural kinds that an individual cannot change into or out of. Furthermore although ‘bachelor’ is not a rigid applier, other apparently nominal kind terms are rigid appliers. For example, I do not imagine that an object that is a television set in the actual world might be something else in another world. Thus ‘television set’ would turn out to be rigid. These considerations suggest that rigid application is a somewhat artificial notion that does not mark off any significant semantic category. In particular it will not help us to distinguish natural kind terms from nominal kind terms. In any case, once we get beyond a few clear central cases of natural kind terms on the one hand and pure function terms like ‘hunter’ on the other, which terms are rigid appliers and which are not is pretty murky and itself rests on controversial metaphysical assumptions. Since we have no clear explanation of what it means for a general term to be rigid and the notion of rigidity with respect to general terms does no work that cannot be done better by clearer notions, I propose that we give up trying to think and talk about general terms as rigid or non-rigid. This distinction just does not usefully apply to general terms. Note that I am not claiming that all, most, or almost all general terms are non-rigid (e.g. see Macbeth 1995), but that the distinction rigid/non-rigid is not appropriate for general terms. General terms may profitably be thought of as indexical or nonindexical, descriptional or non-descriptional, etc. To ask whether a general term is rigid, that is has the same reference or designation from world to world, is a pointless question. A general term, any general term, will mean the same thing when talking about other possible worlds as it does when talking about the actual world. Typically the set of objects to which a general term correctly applies varies from world to world. The way this set gets fixed in the case of natural kind terms is in some ways similar to the way proper names work. As I have argued these similarities are not illuminated by saying that natural kind terms are rigid. The rigid/non-rigid
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distinction is quite useful and indeed indispensable with singular terms, but has been over-extended to general terms.
NOTES 1
For a clear statement of the problem and for references see LaPorte (2000). I am briefly summarizing here. 2 In any case, aside from the obscurity of the notion, kinds do not seem to be the right sort of thing for general terms to designate. The kind, property, or sort tiger would be closer to what we ordinarily mean by a term’s intension rather than its extension. I do not think that terms are usually spoken of as designating their intensions. Furthermore, a statement such as ‘The honeybee is an insect’ is not usually interpreted as being about an individual – the kind honeybee or some such thing – rather it is interpreted as a universal affirmative proposition: ‘All honeybees are insects’. This we now know is necessarily true. Even a statement such as ‘The honeybee = the insect species that is typically farmed for honey’ does not seem to me to be most usefully understood as an identity, pace LaPorte. It also is a universal affirmative proposition: ‘All honeybees are members of the insect species that is typically farmed for honey’. Using ‘the honeybee’ as a way of designating honeybees is a manner of speaking and should not be taken literally as a singular term. 3 See Lewis’ discussion of natural properties (Lewis, 1896, pp. 63–69). 4 There is always a certain amount of confusion in taxonomy and there may be an empirical element in the claim that the honeybee = Apis mellifera in that the term ‘Apis mellifera’ assigns the honeybee to the genus Apis and this is revisable. So the claim that the honeybee is of the genus Apis looks to be necessary and a posteriori, but is not an identity. I discuss this issue below. To see the almostanalyticity of ‘the honeybee = Apis mellifera’ consider what we would say if we discovered that in fact honeybees are robots sent from Mars to spy on us. Would we say that we have in fact discovered that the honeybee is not Apis mellifera? I do not feel comfortable with this. We might, indeed would, say that the honeybee was not aptly named by biologists. But this is different. ‘Apis mellifera’ is somewhat like a complex proper name, like e.g. William Shakespeare. Suppose it turns out that William was not the child of Mr. and Mrs. Shakespeare, but was the legitimate child of Mr. and Mrs. Baker. By the conventions of naming then in force a child takes the family name of his father. So William should have been William Baker – and we might even say in such a case that we discovered that William Shakespeare was really William Baker, although neither he nor anyone else at the time knew it. For all that, ‘William Shakespeare’ would still be a perfectly good name of the bard.
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REFERENCES Abbott, B. (1989): ‘Nondescriptionality and Natural Kind Terms’, Linguistics and Philosophy 12, 269–291. Burge, T. (1979): ‘Individualism and the Mental’, Midwest Studies in Philosophy IV, 73–122. Burge, T. (1996): ‘Other Bodies’, in A. Pessin and S. Goldberg (eds.), The Twin Earth Chronicles, Armonk, NY: M.E. Sharpe. Donnellan, K. (1983): ‘Kripke and Putnam on Natural Kind Terms’, in C. Ginet and S. Shoemaker (eds.), Knowledge and Mind, New York: Oxford University Press. Devitt, M. and Sterelny, K. (1999): Language and Reality, 2nd edn., Cambridge, Massachusetts: The MIT Press. Kripke, S. (1980): Naming and Necessity, Cambridge, MA: Harvard University Press. LaPorte, J. (2000): ‘Rigidity and Kind’, Philosophical Studies 97, 293–316. Lewis, D. (1986): On the Plurality of Worlds, Oxford: Basil Blackwell Ltd. Macbeth, D. (1995): ‘Names, Natural Kind Terms, and Rigid Designation’, Philosophical Studies 79, 259–281. Plantinga, A. (1977): ‘Actualism and Possible Worlds’, Theoria, 254–287. Putnam, H. (1975): ‘The Meaning of “Meaning” ’, in K. Gunderson (ed.), Language, Mind, and Knowledge, Minneapolis: University of Minnesota Press. Salmon, N. (1981): Reference and Essence, Princeton: Princeton University Press. Schwartz, S.P. (1980): ‘Formal Semantics and Natural Kind Terms’, Philosophical Studies 38, 189–198.
Department of Philosophy and Religion Ithaca College Ithaca, New York 14850 USA