Max Kistler
On the Content of Natural Kind
Concepts
Acta analytica
16/17 (1996), pp. 55-79.
Abstract. The search for a
nomological account of what determines the content of concepts as they are
represented in cognitive systems, is an important part of the general project
of explaining intentional phenomena in naturalistic terms. I examine Fodor's
(1990a) "Theory of Content" and criticize his strategy of combining
constraints in nomological terms with contraints in terms of actual causal
relations. The paper focuses on the problem of the indeterminacy of the content
of natural kind concepts. A concept like water
can pick out either a phenomenological property or a scientific one. Moreover,
even on the assumption that the latter is shown to be most adequate, a given
sample will still come out as falling into different natural kinds, according
to the taxomomy of each particular science of which it constitutes an object.
Both chemistry and physics contain concepts which are scientific counterparts
of the common sense concept water,
yet their extensions differ. As a criterion for determining the most relevant
science for a given concept, I suggest to ask which science is most specific
for the typical interactions of the subject possessing the concept, with her
environment. The use of this criterion also permits one to show that a
nomological theory is not necessarily verificationist, contrary to what has
been claimed by Fodor and Boghossian (1991).
According
to Jerry Fodor's Theory of Content
(1990a), the meaning of a 'cow'-token[1] as entertained by
a cognitive system (or in my terminology, the meaning of an instance of the
concept cow) is "cow if (i) there is a nomic relation
between the property of being a cow and the property of being a cause of 'cow'
tokens; and (ii) if there are nomic relations between other properties and the
property of being a cause of 'cow' tokens, then the latter nomic relations
depend asymmetrically upon the former." (Fodor 1990a, p.93). This is the
core of a theory intended to provide a "naturalistic"[2] account of the
semantic relation linking a concept, as represented in a cognitive system, to
its content.
It
seems to me that this core theory, though superior to theories which make the
content of a represented concept depend on the actual causal history of tokens
of that concept[3], is still
unsatisfactory, because it is unable to predict the content of natural kind
concepts in a non-ambiguous way.
The
central idea which I set out to defend in this paper is that a concept like water acquired by a human individual in
a standard manner is, in virtue of natural law, linked to many properties with,
in general, different extensions. One sort of such properties is
phenomenological; its extension is more inclusive than that of any particular
scientific kind. But even on the assumption that the content of a concept is a
"natural kind", in the sense that it is fixed according to a
scientific predicate, there still remains more than one plausible candidate for
this extension. At least this is what I shall try to show for the
paradigmatical case of the concept water.
Even if a "semantic intention", to the effect that the concept in
question be a natural kind concept in a scientific sense, could rule out
phenomenological properties as candidates for determining the extension of the
concept water, this extension would
still come out different depending on whether chemical or physical taxonomy is
considered relevant.
Furthermore,
I shall argue that both of Fodor's proposals for eliminating this ambiguity of
content, namely the "asymmetric dependency condition" (ADC) and the
"actual history condition" (AHC), fail. I suggest that the required
constraint is rather to be found at the level of the implementation of the semantic law linking a concept to the
property it denotes, by a categorizing mechanism.
1. Pure or Mixed Nomological
Theory?
Fodor
does not take a definite stand on the question regarding the ontological level
at which the conditions have to be stated for a concept to have a
well-determined content (extension). On the one hand, Fodor insists on the
importance of the fact that the theory can't rely exclusively on actual causal relations between tokens
of a concept and instantiations of the property it denotes. One reason for this
is that for a nomic relation to hold, it is not necessary that it be
instantiated. Being able to attribute to the concept unicorn a well-defined content even though the property of being a
unicorn is uninstantiated, is "one of the reasons why I want to do the
thing in terms of nomic relations among properties rather than causal relations
among individuals. I take it that there can be nomic relations among properties
that aren't instantiated." (Fodor 1990a, p. 100). If it is true that the
actual causal history of the tokens of a represented concept is irrelevant for
its having content, it should be possible to formulate the theory exclusively
in terms of nomic relations along the following lines.
A
concept C has property P as its content if
(1)
there is a nomic link between C and P (a "semantic law", for short
"SL"), and
(2)
this nomic link satisfies a further restrictive condition.
On
the other hand, on at least two occasions, Fodor reintroduces into the
formulation of sufficient conditions for a concept to have a well-determined
content, a condition (which I shall name the "actual history
condition" or, for short, AHC) to the effect that some actual token of the
concept must actually have been caused in a certain way. The first occasion is
the introduction of the notion of a robust
nomic link which is intended as a strengthening of the ADC[4].
What
role is the ADC supposed to play within the nomological account of content?
Fodor's motivation for introducing it is that it seems to provide a solution to
the "disjunction problem". Perceptual error provides illustrative
examples of the disjunction problem. Fodor proposes to imagine a situation in
which a person entertains the concept cow
as an immediate reaction to seeing a cat which she takes to be a cow. The ADC
is in charge of ruling out the relation between a cat and a token of the
concept cow as an instantiation of a
semantic law (SL). "'Cow' means cow
and not cat or cow or cat, because there
being cat-caused "cow"-tokens depends on there being cow-caused
"cow"-tokens, but not the other way around" (Fodor 1990a, p.
91, his emphasis). The ADC is meant to be an additional condition which can be
substituted for (2) in order to produce a sufficient condition for having a
determinate content.
Now,
my claim is that the ADC does not express an additional requirement over and
above (1), i.e. in this case the requirement
that there be a SL linking the concept cow to the property of being a cow. The ADC expresses only an
implication of that postulate, namely that an instantiation of a different law
linking the concept cow to the
property of, say, being a cat, may result in an exception to the SL. The SL has exceptions as any typical
higher-level law[5] does. Fodor (1974;
1975) has himself given a general account of the relation between natural laws
and their implementation by laws of lower levels, which explains why all (at
least most) higher-level laws have exceptions : an exception to a higher-level
law linking the property F to the property G occurs whenever some of the
lower-level properties which realize
the property F are nomically linked to a property which is not one of those realizing G. The SL's having exceptions is thus a
general feature it has simply by virtue of being a higher-level law; but a
feature shared by (almost) all higher-level laws is definitely too general to
be relevant for explaining the semantic nature of the SL. If a law's having
exceptions suffices for its being semantic, the result is pansemanticism.
In
other words, Fodor's ADC doesn't introduce any constraint over and above
condition (1) because it is implied by the existence of a SL linking concept C
to property P. The asymmetry condition is equivalent to the statement that
exceptions to a SL, and instantiations of more complex laws containing the SL
as a conjunct, are ontologically dependent on the SL, whereas the regular
instantiations of a SL depend only on the SL itself. The ADC is a logical
consequence of the postulate (1), together with a general assumption about the
nature of exceptions. As an implication of (1), the ADC can still be used as a
heuristic device to rule out some causal relations as candidates for the
instantiation of a SL[6], but it would be
misleading to present it as adding a new restriction to the theory.
Fodor
himself points out that there are at least two cases showing that the ADC alone
is not sufficient to guarantee the existence of a meaning relation. We shall
consider them in a moment. To overcome this difficulty, he offers as a
sufficient criterion for determinate meaning a conjunction of the ADC and the
so-called criterion of robustness. The requirement of robustness is one kind of
what I have called an AHC, in the following sense: for A to mean B it is not
only necessary that there is (i) a nomic link between the properties B and A
and (ii) that other nomic links from properties C,D,E... to A are
asymmetrically dependent on the nomic link between B and A, but also that there
has been at least one token of A which was actually caused by something other
than B. "The dependence of As on Bs
is robust only if there are non-B caused As." (Fodor 1990a, p. 118,
his emphasis, variables renamed).
Let
us see Fodor's reasons for introducing an AHC the satisfaction of which should
make semantic nomic relations robust. In at least two sorts of cases there seem
to exist nomic relations on which others are asymmetrically dependent, but
which nevertheless are not semantic relations. First, if a law linking
higher-level properties A and D is implemented by a law linking lower-level
properties B and C, the law A D is asymmetrically dependent
on the law B C; but if A D is a law about airfoils and
B C is Bernoulli's law of fluid
mechanics, the theory should better not predict that B C has a semantic character
(cf. Fodor 1990a, p. 117). Now, why should the criterion of robustness be
helpful in ruling out B C as a semantic law?
Once
again, Fodor's (1974; 1975) own account of the origin of exceptions which
applies to higher-level laws in general leads to the result that most laws
which are at a sufficiently high level are also robust. If B-C is itself a
higher-level law, we should expect that there occur exceptions of the type
which characterizes robustness, namely situations in which C is caused by
something different than B. But it seems plausible that laws implementing a
semantic law are still at a higher level than particle physics; and this is
sufficient to secure the premiss that the laws at the level of B-C are of a
type allowing for exceptions. The robustness criterion does not, in the end,
rule out macroscopic laws - as the law linking B and C - as candidates as
sources of meaning.
The
second sort of case is as pervasive as the first. In a causal chain
instantiating a conjunction of laws, the whole chain is asymmetrically
dependent on its links, i.e. the causal relations constituting it.
"Suppose As (qua As) cause Bs (qua Bs), and Bs (qua Bs) cause Cs (qua Cs),
and assume that As are sufficient but not necessary for the Bs. Then the law A C is asymmetrically dependent
on the law B C. Why doesn't it follow that
Cs mean B?" (Fodor 1990a, p.118). In order to prevent the conclusion that all causal chains become sources of
meaning, i.e. to rule out pansemanticism, Fodor must show two things: first,
that in the general case a causal chain is not robust; and second, that all the
laws implying concepts (as mentally represented) are robust, in the sense that
it is true for all such concepts C, that there has occurred at least one
occasion in which a token of C has been caused by an object which is not part
of C's extension.
The
latter hypothesis is implausible for the following reason. Think of a subject
entertaining a concept representing a shade of green for which there is no word
in the natural language(s) the subject possesses. It seems perfectly possible
that, at least up to a certain time in his life, all tokens of the concept have
been entertained in occasions of veridical perception, i.e. in situations in
which the relevant semantic law (linking the color property to the concept) was
instantiated. It seems simply irrelevant for the question whether the concept
has a well-determined content, whether it has actually been entertained in
virtue of other causal[7] links than the one
linking it to the property constituting its content.
The
former claim is untenable because, once again, there are exceptions. Causes are
not in general necessary conditions for their effects; if Bs cause Cs,
typically there are also situations in which a C has been caused by something
other than a B[8]. It turns out that
causal relations of all types are "robust" in Fodor's sense, not just
those linking concepts to the property they denote.
Thus
it seems as if robustness did not, in the end, constitute the specific
difference permitting one to split the class of all laws satisfying the ADC
into two subclasses: those which are able to ground the meaning relation, and
the others which are not. An AHC, at least of the type proposed by Fodor,
according to which there must be tokens of A which were actually caused by
non-Bs, is incapable of accomplishing this partition.
Robustness
can't play the role of the additional condition (2), because it fails to be
specific for the relation between a (represented) concept and the property it
denotes. We have started from the insight that a theory of mental content which
is based on the postulate of nomic links (SLs) is preferable to a theory which
invokes only actual causal relations
and wholly excludes possible ones. Now, I have argued that a theory which can
be stated exclusively at the nomological level is preferrable to a
"mixed" theory like Fodor's which invokes both nomic links and actual
causal relations in its conditions for a concept having a definite content. In
light of the foregoing discussion, conditions in terms of actual causal links
seem incapable of singling out semantic relations from other nomic relations.
On this record a theory which is stated exclusively at a nomological level
should be preferred, if only for being more parsimonious.
2. Indeterminacy between
phenomenologically and scientifically fixed content
Fodor
proposes two additional restrictions to the core condition (1) of a nomological
theory of content which says that for a concept C to denote a property P, it
must be related to it by a law of nature. We have already seen that the first
restriction, namely the ADC, is redundant (on the premiss that typically,
higher-level laws have exceptions), and that the second restriction, namely
that of robustness, is inefficient. In this section I propose to show that some restrictive condition is indeed
needed if the theory is to be able to account for the fact that natural kind
concepts have a well-determined content. In particular, as long as the theory
contains only the core condition (1), it is unable to predict that the content
of a typical natural kind concept is a "natural kind" in the
scientific sense of this term. It turns out that if such a concept is acquired
in extra-scientific circumstances, its extension is a class of objects (in the
case of "count-concepts", like cow)
or of stuff (in the case of "mass concepts", like gold) which have a phenomenological property in common, but not necessarily a
scientific one. Yet, this doesn't show the concept to be disjunctive, as Fodor
(1990a, p. 104) claims, except in virtue of the question-begging stipulation
that the extension of such a concept must
be determined in terms of scientific predicates.
Let
me argue for this thesis with the help of the following example involving the
concept F. I shall present a story in
which Fodor's theory is bound to predict that the content (in the sense of
extension) of that concept is a phenomenologically specified class of objects.
Confronted with this kind of situation, Fodor (1990a, p. 115) advances the view
that a concept can become a natural kind concept solely in virtue of the intention on behalf of the subject
entertaining it that it should denote a natural kind. Presumably, the
"default intention" when entertaining a general concept is that it
should denote a class of phenomenologically similar objects[9]. I shall argue
that such intentions are powerless to constrain the content of a concept.
Imagine
that Laura has acquired the concept F in contexts in which the perceptually
salient object was a whale. The important feature of the concept F thus acquired is that it does not take
the difference between fish and whales into account. Were Laura to encounter a fish during the period of learning the
concept F (and a word expressing the
concept in Laura's natural language - for ease of exposition I shall take the
language to be English, and the word to be "fish") she would apply
the same concept to it. The concept F is de
facto applied according to a phenomenological taxonomy[10].
Now
imagine Laura encountering for the first time a fish (i.e. one that we would call a fish, according to our
scientific classification of species) and reacting with the utterance
(3)
"That fish is pretty small".
We
can conclude from her using the word "fish" that she applies the
concept acquired as previously described, which she has learnt to associate
with the word "fish". Now, it seems as if there were three
possibilities of judging the truth-value of the proposition expressed by her
utterance (3), depending on what the concept she has acquired[11] denotes[12]:
1.
Either the concept (token) F she expresses with the word "fish"
denotes the property of being a whale (or equivalently, of being a marine
mammal), i.e. does not contain fish in its extension,
2. or
the concept (token) F denotes the property of being a fish, i.e. has as its
extension the class of objects sharing the property of being a fish, which
implies that the animals perceived during her ostensive learning of the concept
were not part of its extension;
3. or
the concept F acquired by Laura is not a natural kind concept (in a scientific
sense), but is rather denoting a phenomenological property G[13] shared by fish and
whales.
How
does a theory which makes mental content depend on nomic relations, rather than
on actual causal links[14], decide between
these options ? As to option 1, it can plausibly be ruled out for the following
reason: the point in replacing actual causal relations as the factor which
determines content, with nomic relations between properties, is precisely to be
able to take relevant counterfactuals into account (Dretske 1983; Fodor 1984,
p. 40). If Laura had encountered (genuine) fish during the learning period, she
would have applied the same concept F to them. That the actual causal history
consists exclusively in encounters with whales is just accidental.
The
same is true for option 2. This is because, on the nomological account, the
situation is perfectly symmetrical between fish and whales. In terms of
counterfactuals, the situation is such that encounters with fish and whales
would have had exactly the same effect on Laura. Therefore, such an account
cannot favor one class of objects over the other, as making up the extension of
the concept acquired.
It
might appear as if we were led into a dilemma, for option 3 seems equally
inacceptable in light of the following consideration: it is plausible to
suppose that in case Laura finds out later on that the animals encountered
first were mammals and not fish, she would conclude that she had made a mistake
in applying the same concept to all of them. That seems to be evidence that she
already misapplied the concept when applying it to whales, and that the concept
is not phenomenological in the end, but denotes only fish. From her own subsequent conviction of having committed
an error, we may conclude that she had the intention to use the concept as a
natural kind concept. But the moment at which she first applies the concept to
a fish precedes her discovery that there is no unique natural kind including
both whales and fish. At that prior moment, the situation turns out to be
rather complex: with respect to the phenomenological concept acquired, she is
correct. She doesn't make the mistake of applying the concept to something not
in its extension; nevertheless she is mistaken in a different way, namely in
supposing that there is a common property shared by whales and fish and which
corresponds to a scientific kind. In other words, according to her own
conceptual system, she applies the acquired concept correctly; she is wrong
only in that the concept she expresses with the word "fish" is not
the same as the concept we express
with that word.
After
all, 3 turns out to be the only acceptable solution among those we considered.
From Fodor's analysis of a similar case[15] we can guess that
he would reject solutions 1 and 2, but that his response would nevertheless
differ from how we presented solution 3. Analyzing a situation described by
Baker (1989) in which a person learns the meaning of a symbol "cat"
in the Language of Thought exclusively through encounters with robot-cats,
Fodor says: "It is OK for some
predicates to be disjunctive as long as not all of them are." (Fodor
1990a, p. 104)[16]. But the analogous
reply to our case would beg the question against the hypothesis that Laura
learns a structurally simple concept which stands for a simple phenomenological
property G.
Fodor
himself doesn't seem satisfied with his answer that the concepts (or,
respectively, mental symbols) acquired in such circumstances are always
disjunctive. Cases like Baker's, Fodor argues, are underdescribed precisely
because usually concepts are acquired
with an intention, appropriate to constrain their content, e.g. to natural
kinds in a scientific sense. But if this reasoning was correct, Fodor would
have to conclude in our case that the concept actually acquired by Laura has no
definite content at all. For Laura's intention
to acquire a natural kind concept is deceived: there in fact exists no one
natural kind whose members share one nondisjunctive property to which her
mental symbol could be nomically related.
For her to be able to exert an influence on
the determination of the content of her concept, what kind of means does she
have at her disposal? There seems to be only one way in which she can
contribute actively to constrain or modify the content of a concept she
acquires. It is her capacity to act
in a way that leads to bringing her in fact in touch with objects or stuff
having different properties, and thus linking the concept being acquired with
these different properties. Laura could have explored her environment more
thoroughly, eventually with the consequence of encountering a fish. But this
variation in her possible experiences is already taken into account within the
nomological theory. It already takes into account all the possible causal relations which could occur during Laura's
acquisition of the concept.
The
analysis of this case brings out two respects in which our account differs from
Fodor's. Firstly, the content of the concept Laura acquires is independent of any possible semantic
intentions. Her intentions to act can indirectly
contribute to shape the content of a concept she acquires, but only through
lawful interactions with her environment, which is what the nomological theory
takes into account from the beginning. But in the absence of a naturalistic
theory of intention, an account of
the acquisition of content could not possibly remain naturalistic if it drew
directly on intentions for fixing the content of a given concept.
Secondly,
Laura's concept is structurally simple. The decisive constraints on content
acquisition are of a cognitive sort. What counts for a psychological, i.e.
empirical, theory of content, is the representational structure actually
acquired: in the way the story is presented, Laura acquires a simple (i.e. non-disjunctive) concept,
which means that we can identify its content only on what we consider to be the
phenomenological level. If the representing structure itself is simple (i.e.
not disjunctive or otherwise logically complex), laws of nature can only link
it to an equally simple property. Without begging the question, there is no
reason not to consider the content as equally simple as the representational
structure itself. And there is such a simple, i.e. non-disjunctive, property
which we can attribute to the acquired concept F, namely a phenomenological
property G shared by fish and whales. According to our scientific taxonomy, the content of Laura's concept F appears as disjunctive. But nothing
forces us to hold that the property which constitues the content of F is a
natural kind of any particular science. The appearance of disjunctivity is due
to a perspective whose adoption is not imposed by the learning situation,
namely that of scientific biological taxonomy.
The distinction between concepts belonging to
common sense on the one hand and scientific taxonomy on the other is not as fundamental
as it might seem. First, the extension of natural kind concepts belonging to
common sense can vary considerably depending on contextual factors. The
variation of the extension of a concept like water is due to a functional component in its content; that is why
a given sample of liquid can count as belonging to the extension of water when the contextually relevant
feature is "flowing in a river", whereas the same sample wouldn't
count as belonging to the extension of the same concept when the contextually
relevant feature is "being drinkable"[17].
Second,
if it makes sense to credit non-human cognitive systems, e.g. animals, with the
possession of concepts, these are neither common sense nor scientific; yet,
their content is determined by constraints analogous to those which are
relevant for our own concepts. I shall discuss the frog's concept of (what we
would call) a fly in the next section.
Third,
even if we assume that the content of a "natural kind" concept (as
represented by a human subject) be determined according to a scientific
standard of what a natural kind is, the requirement alone that there exist a
nomic relation between the concept and a property exemplified in standard
samples alone is in general insufficient to single out a unique content[18]. Even on
scientific criteria, the same sample of stuff (or of paradigmatic objects) is
part of different natural kinds,
depending on which particular scientific taxonomy is considered relevant. We
must, for example, distinguish the (phenomenologically determined) content of water as a common-sense concept from the
content of at least two different scientific concepts: according to chemical
taxonomy, "heavy water", i.e. water molecules containing the hydrogen
isotopes D and T, belongs to the extension of the (chemical) concept water, but not to the concept of water of nuclear physics. This issue
will be discussed in section 4.
3. The content of an animal's
concept
What
is the content of a concept entertained by a non-human cognitive system? Take the
frog's concept of his prey[19]. In this case, the
cognitive structure of the concept-forming subject - the individual frog - is
too inflexible to be able to learn about the difference between flies and
artificial objects looking like moving black dots. The frog doesn't ever learn
to distinguish fake spots from flies, either its perceptual or its conceptual
processes not being fine-grained enough. As it can't in principle, in virtue of its being a frog, find out that
there are in fact two different kinds of object, it is necessary for it to represent them in a uniform
manner, by means of a unique representing structure, namely the activation of
certain ganglion cells in its retina[20], having both flies
and other objects looking like moving black spots in its extension. Let us
assume that this concept is always perceptually triggered, i.e. that the
perceptual mechanism implements the only
law implying it. In particular, it seems plausible that there are no laws of
"thought" linking that concept to other concepts possessed by the
frog. Furthermore, an activation of the fly-concept
is a necessary (though not sufficient[21]) condition for the
frog's flicking its tongue, but it is not linked to any other type of behavior.
This simplicity of structure gives us immediate empirical access to the content
of the concept mediating between the frog's perception and its flicking the
tongue (by holding the additional factors required for triggering the flicking
behavior constant). The content of the frog's concept which is triggered by its
perception of, e.g., flies, is determined by the frog's capacity of determination. The relevant psycho-physical
law is linking a phenomenal quality - being a dark spot of a size between 0.3
and 0.6mm in diameter, moving with a speed within a limited range - to the type
of representing structure (concept) in question. It is not linking the frog to
a natural kind (in any scientific sense), because to distinguish the members of
that kind goes beyond the frog's recognitional capacities. As the latter are
too weak to accomplish discrimination between flies and other objects looking
like moving black dots, his concept appears as disjunctive, by our lights, i.e. relative to our distinctive capacities.
To
anticipate an issue which will be discussed in section 5, the frog example
permits us to show in a particularly clear way that the nomological theory of
the content of concepts is not, despite appearances, necessarily
verificationist. In this example, the cognitive system and its fly-concept under examination are
radically different from the examining subject and his corresponding concept.
The theory would be verificationist if the content of the frog's concept turned out to depend on our (we = the constructors of the theory) capacity to find out (in
principle) about the nature of the objects the frog's concept denotes. But what
determines the content according to the nomological story is what the frog could in principle find out
about the objects denoted. The frog's concept is disjunctive for us, but not for
itself. Another way to express the same idea is by saying that natural kinds
are relative to sciences: with respect to human biology, the content of the
frog's concept of a fly is
disjunctive, but relative to froggy phenomenology (if that were a science) it
is simple[22].
4. Indeterminacy of content
due to the existence of various scientific taxonomies
I
propose to return now to the question of the content of human representations,
in order to defend the following claim. Even if it is granted that a concept
denotes a natural kind property in a scientific sense, this still leaves open
the question of which particular scientific taxonomy is to be considered
relevant.
Let
me use Putnam's (1973, pp.121ff.) famous example of Oscar and twin-Oscar on
their respective planets, being in perceptual contact with H2O and XYZ
respectively. Note first that on a nomological but not on a purely causal
account (i.e. an account relying exclusively on actual causal relations), the
situation comes out the same before and after the discovery of the chemical
structure of water. What counts on the nomological account is how the
conditionals come out: if Oscar
(living before 1750) came to twin-earth and if
he knew a method to tell H2O and XYZ apart, would he represent XYZ as water? On
the causal account there can be a difference in representation only after the discovery of some
differentiating effect by at least someone in the community[23].
Let
us see whether some hypothetical sample of XYZ should be considered part of the
extension of Oscar's concept water.
The answer depends crucially, in a way analogous to Laura's concept F, on whether his concept water actually denotes a natural kind or
a phenomenologically identified kind of stuff. But for the sake of the
argument, let us assume that Oscar possesses a scientific concept, i.e. a
concept whose content is constituted by a natural kind property in a scientific
sense.
Now,
I think that the example of water
permits us to see that this constraint, together with our general presupposition
that content is determined by a nomic link between the concept and a property,
is in general still not sufficient to select one definite extension. The reason
for this ambiguity in content is that different sciences apply different
taxonomies to a given sample of stuff. Consider only chemistry and physics. The
content of the chemical concept water (H2O) is a structurally
complex natural kind, by virtue of chemical taxonomy. Yet it is different from
the content of the corresponding concept water
(H2O) as it appears in the taxonomy of nuclear physics.
More precisely, the property which plays the decisive role in the construction
of the chemical taxonomy is the electronic configuration, responsible for
chemical reactions and the constitution of molecules. Nuclear physics cuts its
kinds according to a finer criterion: it distinguishes, within each chemical
kind, several physical kinds, namely the isotopes. In the taxonomy of nuclear
physics, H2O, D2O and T2O are different kinds. The extension of the narrower physical concept water consists only of H2O, while it
excludes heavy water, i.e. D2O and T2O.
Given
this fact, we have to choose between the following options: either we conclude
that the contents of natural kind concepts as possessed by human subjects are
ambiguous, and determined only relatively to one or the other natural science;
or we look for an additional constraint permitting contents to be determined
uniquely. The latter option seems preferable for it aims at the discovery of an
objective ground for choosing between the alternatives the first option leaves
open. But we can only chose that option if we can justify the idea that the
content of a given concept is determined according to the taxonomy of one
science rather than others. Such a justification can be given on the basis of a
scientific investigation of the interactions of that subject (i.e. of a typical
human) with its environment. With respect to these interactions, it is
reasonable to expect that there exists precisely one scientific taxonomy which
is the most relevant for describing and analyzing them in nomological terms. It
is an empirical question which taxonomy fulfils this criterion for each type of
interaction. The criterion may be less clear-cut than we could have desired, but
it reflects the fact that psychologically, the content of a mental symbol is
not fixed in an absolute manner; rather, it depends on the way the subject in
question lives. As to the interaction of a typical human with water, it seems
plausible to take chemical taxonomy as being the most relevant for it is
precisely the chemical properties of water (as opposed to, for example, the
cross-section of water-molecules for their interactions with neutrinos) which
are decisive for the role this substance plays for human physiology[24]. As a consequence,
the physical concept water (H2O) which excludes heavy water (D2O and T2O) from its
extension, should be considered a different concept from the commonly held one
whose content is determined according to the chemical taxonomy. The physical concept is the most specific one
only in circumstances where these differences play some role for the subject (as might happen, e.g.,
to an engineer in a nuclear power plant).
On
the other hand, from the fact that the chemical level is the most relevant for
the commonly held natural kind concept
water (remember our assumption that Oscar possesses a natural kind concept
in a scientific sense, but without deciding in advance according to which
particular science), we can conclude that the discovery of the H2O-nature of water
didn't lead to the creation of a new concept (admitting that before the
discovery, there already existed a natural kind concept, as opposed to the
corrresponding phenomenological one); rather, it permitted us to refine the
knowledge of the identity conditions of the kind already picked out. On the
basis of our criterion, XYZ can be excluded from the extension of water because, by hypothesis of that
thought experiment, there exists a (chemical) difference: different elements
are by definition chemically distinct, and so are molecules constituted by
atoms of different elements. Whether this difference is already discovered in a
given situation is not decisive in the framework of the nomological account.
5. The threat of
verificationism
The
content of a concept as it is represented in a cognitive system is contingent
upon the categorizing mechanisms of that system. In this last section, I would
like to show that Fodor's (and Boghossian's 1991) conviction that a nomological
theory of content is necessarily verificationist
is due to a misunderstanding of the implications of this contingency. It is a
matter of empirical research to find out about the content of a given
(represented) concept, but that doesn't make its content itself depend on the
finding out. This becomes clear if one takes care to distinguish the
representational system under examination from the representational system of
the researcher who is trying to find out about the content of a concept
entertained by the former. The content of the former's concept does not depend
on the latter's finding out about it, yet the theory would be verificationist
only if it predicted that this were the case.
I
propose to take a closer look into why this is so by comparing the hypothetical
substances XYZ and ABC. Boghossian (1991) proposes to imagine a situation which
is slightly different from that imagined by Putnam (and which Fodor 1991,
p.274, finds "much more
outré", his emphasis): what should we say in the counterfactual situation
where there is a substance whose behavior is so similar to that of water that
it can in principle never be detected
by humans as differing from usual water (this impossibility may be due to the
limited capacities of the human body).
The
criterion we stated above was the following: the content of a concept is to be
determined by an ideal taxonomy at the level of the science which is most
specific for the interactions of the examined subject with its environment. On
the basis of this criterion the ABC thought experiment should be analyzed as
follows: as it is described by Boghossian, the difference between H2O and ABC can only
be physical. (In fact, he proposes that the only circumstances on which ABC
behaves differently from H2O be realized in black holes, which are actually
places where physical differences show up, even among substances without
chemical differences.) This means that ABC is in the extension of the concept water because, at the level most
relevant for humans in ordinary life conditions, water is a
"chemical" concept. Chemical discoveries about the stuff it denotes
are relevant for the delimitation of its content, but physical discoveries
about eventual variations within the
chemically individuated kind aren't.
Boghossian
argues that this case brings out the verificationist implications of the
nomological theory. According to him, we should want to exclude ABC as well as
XYZ from the extension of water; yet
he holds that a nomological theory doesn't have this option open to it, for
there is, in that case, no possibility of verification and thus no possible difference in the concepts
formed upon encounter of H2O on the one hand, and ABC on the other.
I
have already explained why I think it is wrong to assume that we should want to
exclude ABC from the extension of our concept water. But concerning the alleged verificationist character of a
theory of mental content, there is a more general lesson to be drawn. Not all
of what we - as constructors of a
psychological theory - find out about water, and especially about further
distinctions and sub-taxonomies within that kind, counts for the determination
of the content of the examined subjects' representations. This may be slightly
confusing because here object and subject of examination are of the same
(human) kind, and possess the same capacities of discrimination. The difference
comes from the fact that as a theory constructor the psychologist (or, for that
matter, the semanticist) has access to natural kind concepts figuring in different
sciences - there being more than one concept of water, according to whether the relevant taxonomy is considered to
be physics, chemistry or still another science. But, to be able to escape
ambiguity it suffices to note that the content of the natural kind concept water is completely determined by the
(actual and possible) chemical
behavior of the substance with which a typical human is causally interacting.
Both
Fodor and Boghossian are convinced that the nomological theory has a
verificationist character because it determines the content of concepts as they
are represented by a subject, in terms of the capacity of discrimination the
subject can possibly acquire (given the social and historical circumstances of
his life), concerning the objects (or the stuff) in its extension. They take it
that this means that what we may find
out about those objects is relevant for the determination of the class of
objects denoted by the concept as possessed by
the examined subject. But that suspicion of verificationism is due to a
confusion between the two discriminatory capacities, of the categorizing
mechanism linked to the concept of the examined
cognitive system and of the corresponding concept of the examining subject.
Let
me briefly comment on a move Fodor makes in this context, and which has some
relevance to the topic discussed in section 1 of this paper. Whereas Boghossian
thinks that the alleged verificationist implications make the theory hopeless,
Fodor tries to amend it in the following way. He tries to attenuate (what
appears to him as) the verificationist aspect of the theory by introducing a
supplementary condition for a concept C to denote a property P: some of the objects instantiating P -
which make up C's extension - must actually
figure in C's causal history. According to this new version of an AHC[25], at least one
C-token must have been entertained as a causal consequence of triggering by
(perception of) a P in the environment. The "mixed" theory resulting
from the addition of the AHC to the pure nomological theory[26], is still,
according to Fodor, "a soupçon verificationist", yet to a degree he
finds tolerable.
But
if the theory actually were (necessarily) verificationist - which I think it is
not - the introduction of the AHC could not provide a cure against this fact.
At this point, Boghossian correctly remarks that the AHC "doesn't
ultimately help with the problem about verificationism" (Boghossian 1991,
p. 76f.). It restricts the possible extension of a symbol to objects of a kind
which has actually come in causal contact with the subject entertaining this
symbol. But, first, such a fact from the personal history is highly accidental
and leads to the consequence that we don't actually possess any primitive
concepts of kinds we have not yet directly observed. However it should not
depend on my having been to the zoo whether my concept penguin is primitive or not, or (if we admit that it is primitive)
whether I can even possess that concept at all before having been to the zoo.
Second, the AHC doesn't appear to be relevant to the point about
verificationism. It suffices to imagine that there be ABC (or, for that matter,
D2O) molecules in our
actual environment - then we have been in actual contact with these
non-standard particles of "water"; but that doesn't change anything
with respect to the question of whether we should or should not count them as
falling in the extension of water,
i.e. whether their presence has any influence on the content of this concept.
5. Conclusion
I
have been supposing throughout this paper that the search for a nomological
account of what determines the content of natural kind concepts is an
interesting part of the general project of "naturalizing" intentional
phenomena, i.e. explaining them in naturalistic terms. If the content of the
concepts possessed by a cognitive system were completely determined by the
actual causal relations to which that system is exposed, that would make the
content of its concepts depend on the accidental circumstances of its experiences.
Fodor is right in trying to formulate a theory of the content of concepts at a
nomological level. But so far, he has stated only a core condition of a
nomological theory which doesn't contain sufficient constraints to let the
content of a concept like water come
out non-ambiguous. First, his proposal for the way of handling the disjunction
problem, namely the asymmetry condition, is in fact not a new constraint, but a
consequence of the analysis of denotation as a nomic relation. Second, I have
tried to show that Fodor is unsuccessful in adding conditions of actual causal
history as further constraints. They are not able to resolve the indeterminacy
of content which remains once it is assumed that laws of nature fix the content
of a concept.
There
are two kinds of indeterminacy. First, a "natural kind" concept,
whether of countable objects like fish or of a substance like water, can, in a
human conceptual system, pick out either a phenomenological property or a
scientific one. Second, even on the assumption that some constraint can be
found which selects one of these options, the content of the concept is still
indeterminate. In the case of a scientific natural kind concept, a given sample
will come out as falling into different natural kinds, according to the taxomomy
of each particular science of which it constitutes an object. Both chemistry
and physics contain concepts which are scientific counterparts of the common
sense concept water, yet their
extensions differ.
I
suggest that what actually provides sufficient contraints to make the
denotation of concepts (as they are represented in a particular cognitive
system) non-ambiguous, is the categorizing mechanism to which they are linked.
The categorizing device linking the concept to the property which is constitutive
of its content, is essentially a triggering mechanism sensitive to this
specific property, or combination of properties, such that its capacity of
discrimination is a matter of objective fact. It is the implementation of the
nomic link by such a categorizing mechanism which determines content
non-ambiguously.
Finally
I tried to show that a nomological theory is not necessarily verificationist,
if it is understood as a (framework for a) psychological theory. As such, it is
empirical and its truth has to be evaluated with respect to particular (human
or animal) subjects. Their
discriminative capacity in virtue of which they can eventually detect
differences within the class of objects which one of their concepts denotes,
plays a role for the determination of the content of this concept; but what
would make the theory verificationist and what is not the case, is that our (as subjects of psychological
research) possibilities to do so count for the determination of the content of
the concept possessed by the examined
cognitive system.[27]
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[1]The issue of the origin of the
meaning relation can be dissociated from Fodor's (1975) hypothesis that the
concepts represented by a cognitive system are organised as a "Language of
Thought" (LOT). So when Fodor speaks of a 'cow'-token, for him this is not
only a concept, but a word in the hypothetical LOT. The present paper, however,
focuses only on the conditions under which this entity, whether it has the additional
property of being a word in a LOT or not, can be considered a token of the
concept cow. (I shall designate
concepts by the name of the property they denote, in italics.)
[19]The frog can be said to possess this
"concept" in the sense intended throughout this paper, namely that of
a structure (in the frog's case, the activation of certain ganglion cells in
the retina) covarying lawfully with a property of the environmment, namely a
pattern of light. To be sure, the content of a concept in this sense can't be
identified with a "conceptual role" because it is presumably not part
of a larger network; therefore, there are no interactions according to which
such roles could be defined. For present purposes, I share Fodor's assumption
(for an explicit defense, see Fodor and LePore 1991, Fodor 1994) that concepts
can be individually individuated, even if the process of their acquisition, during the individual's
ontogenesis, is holistic (for evidence on the latter fact, see Bloom 1994).
Compare Block according to whom it is a plus for a theory of what meaning is if
it also tells us what it is to know and learn meanings (Block 1990, p. 150). It
is a plus that Fodor's theory certainly lacks: it shares this feature with all
atomistic theories of meaning.
[27]I would like to express my thanks
for helpful comments and discussion to Julius Moravcsik, Joëlle Proust,
François Recanati, and William Taschek, to my auditors in Saarbrücken, Germany,
and Karlovy Vary, Czech Republic, where I have presented parts of an earlier
version of this paper, and to Marcel Lieberman who kindly corrected my English.