Joanna Odrowąż-Sypniewska
Published in: Sprache und Welt. Language and Word. Pre-proceedings of the 32nd International
Wittgenstein Symposium, Kirchberg am Wechsel 2009.
Rigidity and Essentialism
Abstract
According to the semantic conception of rigidity a given kind term is a rigid designator iff it
designates the same kind in all possible worlds. According to the metaphysical conception a
kind term is a rigid applier iff it is such that if it applies to an object in any possible world,
then it applies to that object in every possible world. Both conceptions face serious
difficulties. It is widely assumed that natural kind terms should be rigid, while other kind
terms should come out as non-rigid. The main problem for the metaphysical conception is
that according to the current biological conceptions of species membership in a species is not
essential to its members. Hence, biological kind terms are not rigid appliers. In his recent
paper Devitt tries to resurrect biological essentialism. I argue that while Devitt’s argument is
very persuasive, it does not succeed.
1. Introduction
The notion of rigidity has been introduced and defined for singular terms by Kripke. In
Naming and Necessity Kripke also suggests that this notion applies to some general terms –
namely to natural kind terms. He does not however state precisely how general term’s rigidity
should be understood. Scott Soames has argued that extending the notion of rigidity from
names to natural kind predicates is one of the two important pieces of “the unfinished
semantic agenda that has been left to us by Saul’s Kripke Naming and Necessity” (Soames
2002, 3).
In Naming and Necessity we can find two criteria of rigidity. According to the first, “N” is a
rigid designator if in every possible world it designates the same object. According to the
second, “N” is a rigid designator if “N might not have been N” is false (this is so called
“Kripke’s intuitive test”). For singular terms both criteria give the same result. Any singular
term which is rigid according to the first criterion, will be rigid according to the second, and
vice versa. However, in the case of general terms those criteria come apart. The first criterion
leads to the semantic conception of rigidity, whereas the second – to the metaphysical
conception. Let us look at the semantic conception first.
2. Semantic conception of rigidity
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It seems that the simplest way of extending the notion of singular term’s rigidity to general
terms is to claim that a general term is rigid if it has the same extension in all possible worlds.
However, such an interpretation is a non-starter since according to this definition barely any
general terms are rigid. For instance, since the number of elephants in different possible
worlds varies, the term “elephant” is not rigid on this account. The same applies to the
majority of natural kind terms. The only rigid general terms would be some mathematical
terms and terms which are necessarily empty. Another way of extending the first criterion to
general terms is to argue that a given kind term is a rigid designator if it designates the same
kind (property, category, etc.) in all possible worlds. The main problem for this conception is
that all kind terms come out as rigid designators and rigidity is trivialized. Terms such as
“honeybee”, “the species typically farmed for honey”, “bachelor”, “the kind most commonly
broached in discussions about analyticity” are all rigid since they refer to the same kind
(HONEYBEE, THE SPECIES TYPICALLY FARMED FOR HONEY, BACHELOR, THE KIND MOST
COMMONLY BROACHED IN DISCUSSIONS ABOUT ANALYTICITY
respectively) in all possible
worlds. In order to avoid that consequence one may distinguish between different uses of kind
terms (cf. LaPorte 2006). Terms “bachelor” and “honeybee” have only rigid uses, whereas
expressions “the species typically farmed for honey” and “the kind most commonly broached
in discussions about analyticity” have rigid as well as non-rigid uses. “Honeybee” in all of its
uses refers to the kind HONEYBEE, whereas “the species typically farmed for honey” on some
uses refers to the kind THE SPECIES TYPICALLY FARMED FOR HONEY and on some to the kind
HONEYBEE.
So, one may argue that general terms are rigid if in all their uses they designate
the same kind in all possible worlds. The problem with this solution is that rigid will be the
non-natural kind term “bachelor” as well as the natural kind term “honeybee”. On the other
hand terms such as “bald happy human” will also be rigid, for they have only rigid uses: “bald
happy human kind” in each possible world refers to the BALD-HAPPY-HUMAN kind (cf.
LaPorte 2000). It constitutes a problem since rigidity is supposed to be a feature that
distinguishes natural-kind from non-natural kind terms.
Moreover, on the semantic conception each complex term used descriptively has a rigid use.
That is why S.P. Schwartz accused LaPorte of “confusing rigidity with consistency of
meaning” (Schwartz 2002, 272). LaPorte argues that although it would be “a confusion to say
that an expression is rigid just because it keeps the same meaning from world to world”, his
view “does not fall into this confusion” (LaPorte 2006, 329). “The species typically farmed
for honey” has rigid as well as non-rigid uses, so it is not rigid, although it keeps the same
meaning in all worlds. However, it seems to me that on LaPorte’s account any complex term
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has a rigid use “just because it keeps the same meaning from world to world” and this is
dangerously close to confusing rigidity with constancy of meaning. In addition such a view
has a bizarre consequence. Any complex term which does not refer to any natural kind will be
rigid. For instance, the term ‘bald-happy-human kind’ is rigid, because BALD-HAPPY-HUMAN
kind is the only kind for it to refer to. The term “large carnivorous quadrupedal feline, tawny
yellow in color with blackish transverse stripes and white belly” (cf. Kripke 1980) is rigid, if
there is no kind which fits that description and it is not rigid if there is a kind that does fit it.
So the more gerrymandered the kind the bigger the chance of it being rigid. Such a
consequence is extremely counterintuitive.
3. Metaphysical conception of rigidity
According to the metaphysical conception a kind term is a rigid applier iff it is such that if it
applies to an object in any possible world, then it applies to that object in every possible world
(in which the object exists) (Devitt 2005, 146).1 On this view “bachelor” will not be rigid
because someone who is a bachelor in the actual world need not be a bachelor in a nearby
world. However, it has been argued that rigidity so-understood does not mark out the class of
natural kind terms either, because biological kind terms will come out as non rigid. According
to most contemporary conceptions of species membership in a species is not essential to its
members. Recently LaPorte (2004) and Okasha (2002) have argued that on none of the viable
conceptions of species intrinsic properties are decisive as far as species-membership is
concerned. The essence of biological natural kinds is relational (on interbreeding and
ecological conceptions) or both relational and historical (on the phylogenetic conception).
Since relational properties are rarely essential to objects that have them, it is argued that
belonging to a particular species is not essential to its members. Therefore a member of a
given species in our world may belong to another species in another possible world. So – if
relational species theories are correct – on the metaphysical conception of rigidity none of
biological kind terms will come out as rigid and rigidity so understood will become useless as
a mean of distinguishing natural form non-natural kind terms.
However, in his recent paper Devitt tries to resurrect biological essentialism and argues that
essentialism is consistent with current biology (Devitt 2008). According to Intrinsic
An alternative formulation says that “a predicate P is essentialist iff for all worlds w and any object o, if P
applies to o in respect to w, then P applies to o in all worlds in which o exists”. (Soames 2002, 251). On both
formulations it is evident that rigidity is akin to essentiality.
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Biological Essentialism (henceforth IBE) Linnaean taxa have essences that are, at least partly,
intrinsic underlying properties. Devitt distinguishes three problems: the taxon problem, the
category problem and the conspecificity problem, and claims that while relational species
concepts give answers to the category problem, it is IBE that provides an answer to the taxon
problem. The taxon problem (T) is a problem of what is it to be a member of any group that
happens to be species. (i.e. “What makes an x an F?”). The category problem (C) is a problem
of what is it for a group to be a species (i.e. “What makes Fs a species?”). And finally the
conspecificity problem (CS) concerns the question “In virtue of what xs are in the same
species?” Devitt argues that relational species concepts do not answer (T), for none of the
conceptions appealing to relational essences of species gives any account of species identity.
They say how the notion of “tiger” is to be understood (e.g. on the phylogenetic conception it
is a lineage of a certain sort), but they do not say in what being a tiger consist. According to
Devitt the only conception well fitted to answer (T) is IBE. Moreover, IBE can be wedded to
relational species concepts so that they together are able to answer all the problems.
Devitt says that a relational nonintrinsic answer to (CS) would imply a relational nonintrinsic
answer to (T) but – contrary to what might seem – a relational answer to (C) given by
relational species concepts does not imply a relational nonintrinsic answer to (CS). Relational
species concepts, such as e.g. Biological Species Concept (BSC), do not say in virtue of what
organisms belong to the same species. According to BSC a given organism is conspecific with
organisms with which it can interbreed, but – as Devitt points out – this is not to say that
organisms are conspecific in virtue of interbreeding. This is why BSC can be wedded to IBE.
IBE coupled with BSC would claim that because the members share the intrinsic properties
necessary to make them conspecific, in the given environment they interbreed and hence have
the property that makes them a species according to BSC (cf. Devitt, 2008, 365-6). Hence,
while BSC provides an answer to the category problem, IBE answers the taxon problem and
IBE and BSC together answer the conspecificity problem. Since the answer to the last two
problems is (at least partly) intrinsic, the claim that belonging to a species is essential to its
members can be rescued and biological kind terms may be regarded as rigid.
There is a couple of problems with this solution.2 Firstly, even if it seems plausible for BSC, it
is much more problematic for other relational species concepts. If we wanted to combine IBE
with the ecological conception, we would be forced to defend a rather controversial claim that
it is in virtue of sharing the intrinsic properties necessary to make the organisms conspecific,
2
A separate problem is the worry that IBE postulates intrinsic essences not recognized by biology, but I will not
address this worry here. See e.g. Okasha 2002.
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that they occupy the same ecological niche. In case of the phylogenetic conception, Devitt
writes that “an organism is a member of a certain species F in virtue of having a certain
intrinsic property and being part of a particular genealogical nexus” (Devitt, 2008, 368). Such
an answer implies that both intrinsic features and genealogical history are needed for
conspecificity, and this seems inconsistent with current biological theories.
Secondly, although distinguishing (T), (C) and (CS) is indeed very important, the weight that
Devitt attaches to (T) is much greater than the weight attached to it by relational species
theorists. For such theorists an answer to (T) is a sort of by-product of the answer provided to
(C) and (CS), whereas for Devitt (T) is of primary importance.
BSC answers the category problem (C) by saying that a group of Fs is a species if they
interbreed. Of course those organisms that interbreed have certain underlying intrinsic
properties that are worthy of investigation. If we find out that there are intrinsic properties that
are shared by all and only the members of F (although according to current biology this is
unlikely) then we may say that those intrinsic properties are characteristic of the members of
F and together they constitute the (partial) answer to the taxon problem (T). However, such
intrinsic properties are only of secondary importance. If the organisms in question will cease
to interbreed they will cease to be a species, notwithstanding the fact that they will continue to
share the intrinsic properties. Similarly, if the organisms start to interbreed with other
organisms that have different intrinsic properties, the species F will expand and its intrinsic
characteristics will change. Hence, saying that it is intrinsic properties that make the xs the Fs
is misleading. If Fs constitute a species, then since membership in a species depends on
relational properties and such properties are not essential to members of the species,
membership in F is not an essential feature of its members. They may retain all their intrinsic
properties but change membership and cease being the Fs.
It seems to me therefore that while Devitt’s argument is very persuasive, it does not resurrect
essentialism and does not help interpret “rigidity” in such a way that it distinguishes natural
from non-natural kind terms.
4. Conclusion
Both conceptions of rigidity – the semantic one and the metaphysical one – face serious
difficulties. Neither fulfils Kripkean postulate that nearly all natural kind terms are rigid and
most of the others are non-rigid. The prospects of resurrecting biological essentialism, which
is needed to make the rigid application view viable, are dim. Hence, I agree with Soames
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when he says that “it might be advisable to reserve the terminology of rigidity exclusively for
singular terms” (Soames 2002, 263).
Literature
Devitt, Michael 2005, “Rigid Application”, Philosophical Studies 125, 139-165.
Devitt, Michael 2008, “Resurrecting Biological Essentialism”, Philosophy of Science 75, 344382.
Kripke, Saul 1980, Naming and Necessity, Oxford: Basil Blackwell.
LaPorte, Joseph 2000, “Rigidity and Kind”, Philosophical Studies 97, 293-316.
LaPorte, Joseph 2004, Natural Kinds and Conceptual Change, Cambridge: Cambridge
University Press.
LaPorte, Joseph 2006, “Rigid Designators for Properties,” Philosophical Studies 130, pp. 32136.
Okasha, Samir 2002, “Darwinian Metaphysics: Species and The Question of Essentialism”,
Synthese 131, 191-213.
Schwartz, S.P. 2002, “Kinds, General Terms and Rigidity: A Reply to LaPorte”,
Philosophical Studies 109, 265-277.
Soames, Scott 2002, Beyond Rigidity: The Unfinished Semantic Agenda of Naming and
necessity, New York: Oxford University Press.
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