Saturday, February 05, 2005

Concepts I: The Classical View

In response to my most recent plea for requests, Clark wrote:
I'd be interested in how cognitives looks at the problem of reference. Does cognitive science tend to be internalist or externalist and how does it deal with the "world out there."
I started to try to address this, but began to realize that each time I did so, I had to assume more knowledge of cognitive theories of concepts in readers than is probably reasonable. So, in order to get to a discussion of reference, I want to start with a discussion of theories of concepts. It may even become clear how cognitive scientists, or at least those cognitive scientists who study concepts, deal with reference and "the world out there" by the time we're done with the background. If not, then I can talk about that more directly afterwards.

Before I get started, I should note that the terms "concepts" and "category" are painfully ambiguous in the cognitive scientific literature. Bertrand Russell once remarked1:
What, exactly is meant by the word ‘category’, whether in Aristotle or in Kant and Hegel, I must confess that I have never been able to understand.
He might as well have substituted classical, prototype, and exemplar theories for Aristotle, Kant and Hegel, because the use of term "category," along with "concept," is very difficult to pin down in cognitive science. Because the terms "category" and "concept" are used pretty much interchangably in the literature, I'm going to do the same, but I'm not going to make any attempt to try to define either term, so you'll just have to deal with the ambiguity.

Cognitive scientists who study concepts are generally concerned with three issues: how concepts are represented, how we classify instances (which I will call exemplars from here on out) as belonging to a concept, and how we use concepts in reasoning. Of course, cognitive scientists aren't the first to address these issues. Since the days of Plato and (more importantly for our purposes) Aristotle, the nature of concepts, in their representations, how we recognize exemplars of particular concepts, and how we reason with concepts, has been one of the most studied issues in philosophy. And since the days of Aristotle, one view of concepts has dominated. Under that view, which is now commonly referred to as the classical or definitional theory of concepts, concepts are defined by a set of necessary and sufficient features. In this post, I'm going to discuss the classical theory of concepts, and it's many (many, many) problems. In subsequent posts, I'll talk about the theories that have replaced it, starting with the two main types of similarity-based theories (prototype and exemplar theories), and then moving on to more recent theories that attempt to account for some of the deficiencies of similarity-based accounts. If, by the end of this series of posts, you haven't become fully aware of the incredibly muddled state of concept research, then I will have failed to do my job.

Concepts: The Classical View

For both Plato and Aristotle, concepts were defined by their essences. While Plato's focus on ideal forms doesn't exactly lend itself to scientific theories of concepts, many theories of concepts in the first half of the 20th century (such as those one might find among the logical positivists) were similar to Aristotle's, in that they treated concepts as being defined by a set of empirically-discoverable (though sometimes not directly observable) necessary and sufficient features. This view of concepts is actually very powerful, and provides a simple account of several features of concepts that any theory must explain. For instance, it provides a straightforward explanation for how we separate members of a category from non-members. Members of a category are just those exemplars that exhibit the necessary and sufficient features that define the category, and any exemplars that do not exhibit those features are not members of the category. It also provides for an intuitive account of concept formation. We form concepts by encountering many examplars, and extracting the features that unequivocably divide these exemplars into separate classes. Finally, as researchers studying semantic networks in the 1960s and 70s showed2, the classical theory provides a nice way to construct taxonomic relationships between concepts. Members of a taxonomy are related by their necessary and sufficient features, with more subordinate members being defined by the same features that define their superordinates, along with an additional set of features that distinguishes them from other superordinates.

It was the power and intuitive appeal of the classical theory that allowed it to survive relatively unchallenged for more than 2 millenia. However, in the 1950s, the classical view began to come under attack from philosophical circles, and by the end of the 1970s, there were few cognitive scientists who still held it. The criticisms are many. In 1951, Quine famously criticized the classical account because of its attachment to the analytic-synthetic distinction. Around the same time, Wittgenstein's criticisms of definitions were also being published. As everyone knows, he used GAME as an example of a concept that admits no definition. Subsequent research has shown that concepts like GAME are not exceptions to the general rule that concepts are defined by their necessary and sufficient features, but that in fact, definitions may not exist for any real-world concepts. Take, for example, the concept BACHELOR, which has often (even by Quine) been used as an example of a concept which is clearly defined by a set of necessary and sufficient features. For BACHELOR, those features are male and unmarried, and thus the definition of BACHELOR is "an unmarried male". Yet, if we adopt the classical view, and treat this as the concept's representation, we immediately begin to run into problems. First of all, unmarried male children are not bachelors, and neither are people who've been married and are no longer, so we must amend the definition by inserting the word "adult" between "unmarried" and "male," and perhaps change the wording a bit to make it clear that bachelors are adult males who've never been married. Then, we have to come up with a qualification in the definition that allows us to exclude many other types of individuals. For instance, are middle-aged gay men who have been in monogomous relationships for years bachelors? What about priests? Most of us probably feel that neither of these types of individuals classify as bachelors, and if we thought a little, we could probably come up with a whole host of other types of individuals that fit the definition, but that we wouldn't classify as bachelors. In the end, we're going to end up with a really long set of disjunctive rules to keep out all the non-bachelors who fit with our first definition of bachelors. Unfortunately for adherents of the classical view, the same is probably true of every other everyday concept as well.

There may be other philosophical problems for the classical view, as well. As Eric Margolis and Stephen Laurence have argued3, the classicical view is really just an instance of a descriptivist theory of reference, within which concepts refer to descriptions of real-world instances. For this reason, they believe that the classical view is subject to the same criticisms that Kripke4 and Putnam5 use against descriptive theories of reference. The primary criticism is that it is possible to discover that our descriptions, or definitions, are wrong. I'm not so sure that this is a problem for cognitive psychological versions of the classical theory, however. Since psychologists argue that the discovery of the essences, or definitions, of concepts is a learning process, it stands to reason that our representations of concepts can be erroneous. Even if we do no have all the information about the class to which a concept refers, we could still represent the concept with a definition, and when we discover that parts of our definition are erroneous, we can revise our representations.

Even if adherents of the classical view can get around Kripke and Putnam's arguments, the lack of definitions, and Quine's problem of analyticity, are pretty damning. However, the philosophical problems are nothing compared to the psychological ones, and there are many of those. First, when queried, people are rarely able to produce definitions of the concepts they employ6, and when they do produce definitions, they often differ greatly both across subjects and for the same subject over time7, making it difficult to explain how people are able to communicate or reason about concepts over time, if they represent concepts as definitions. In most cognitive versions of the classical theory, definitions are represented in the form of rules, with Boolean disjunctions representing the set of necessary and sufficient features. However, researchers have shown that people are not conscious of the rules that define many concepts, and that some concepts may not be represented by any sort of rule8. Furthermore, if there are definitions, but they must account for a large number of problem instances (e.g., the gay males and priests in the BACHELOR example), then definitions will become increasingly difficult to learn. In fact, by the time you add all the Boolean disjunctions necessary to define a concept as simple as BACHELOR, you've probably made the defininition unlearnable.

Experiments designed to test the classical theory have failed to show evidence of definitions as well. For instance, when participants are presented with one concept (like BACHELOR), their reaction times are no slower for that concept than for concepts that make up part of their definition (e.g., MALE)9. Since, under the definitional view, the complexity of a concept should be a function of the complexity of the concepts that are used to define it, we would expect reaction times to be slower for BACHELOR than MALE. Perhaps the most damaging empirical finding, however, was that of typicality effects. Elanor Rosch and her colleagues10 conducted several experiments demonstrating that some exemplars (e.g., robins as a member of the category bird) are treated as better members of a category (i.e., more typical) than others (e.g., penguins or kiwis... sorry Richard). The persistence and predictive power of typicality poses a serious problem for any definitional account. If concepts are represented only by their definitions, then exemplars are either exhibit those features or do not, and thus are either members of a category or not. This was one of the positive qualities of classical theories above, but after Rosch's research, it makes the classical view difficult to retain. Any additional information added to the concept to account for typicality effects would have to be something other than a definition.

If the existence of typicality effects weren't enough, further research in the 1970s demonsrated that category membership is often not a binary relation (an exemplar is either a member of a category or it is not). Instead, category boundaries tend to be fuzzy, and there is a great deal of both inter-subject and intra-subject disagreement about category membership, about whether a particular exemplar is a member of a category11. Once again, this goes against the all-or-none membership that the classical theory predicts.

So, by the beginning of the 1980s, the consensus among cognitive scientists was that it was time to get rid of the classical theory. Many, especially Rosch and her colleagues, had been developing alternative theories since the mid-70s, which treated categories not as definitions, but as family-resemblance structures, and category membership was determined by determining the similarity between an exemplar and the features used to represent the concept. The period between 1975 and 2000 can probably be called the age of the similarity-based views (which is not to imply that they are not still prominent, just that there weren't really any alternatives until recently). There are two general types of similarity-based views, prototype theories and exemplar theories. In the next post, I'll discuss prototype theories. After that, exemplars.

1 Russel, Bertrand (1946). A History of Western Philosophy. London: George Allen & Unwin.
2 Collins, A.M., & Quillian, M.R. (1969). Retrieval time from semantic memory. Journal of Verbal Learning and Verbal Behaviour, 8, 240-247.
3 Margolis, E., & Laurence, S. (2003). Concepts. In Stich, S. P. (Ed.), Blackwell Guide to Philosophy of Mind.
4 Kripke, S. (1980). Naming and Necessity. Cambridge, MA: Harvard University Press.
5 Putnam, H. (1975). The Meaning of 'Meaning'. In K. Gunderson (Ed.),
Language, Mind and Knowledge. Minneapolis: University of Minnesota Press.
6 McNamara, T.P., & Sternberg, R.J. (1983). Mental models of word meaning. Journal of Verbal Learning and Verbal Behavior, 22, 449-474.
7 Rosch, E. (1975a). Cognitive representations of semantic categories. Journal of Experimental Psychology: General, 104, 192-233.
8 Maddox, W.T., Filoteo, J.V., Lauritzen, J.S., Connally, E., & Hejl, K.D. (In Press). Disontinuous Categories Affect Information-Integration, but not Rule-Based Category Learning. Journal of Experimental Psychology: Learning, Memory, and Cognition.
9 Fodor, J. A., Garrett, M., Walker, E., & Parkes, C. (1980). Against Definitions. Cognition, 8, 263-367.
10 Starting with Rosch, E. (1973). On the internal structure of perceptual and semantic categories. In T. E. Moore (Ed.), Cognitive Development and the Acquisition of Language. New York, Academic Press.
11 McCloskey, M., & Glucksberg, S. (1978). Natural Categories: Well-defined or fuzzy sets? Memory and Cognition, 6, 462-472. Barsalou, L. (1989). Intraconcept similarity and its implications for interconcept similarity. In S. Vosniadou & A. Ortony (Eds.), Similarity and Analogical Reasoning.

10 comments:

Anonymous said...

"(e.g., penguins or emus... sorry Richard)"

Not to worry, I'm a Kiwi ;)

Fascinating post, by the way. I've just one quick question for now: what do you mean by "within subjects disagreement"? Will individuals disagree with their earlier selves about category memberships? Or does it just mean that they can't make up their minds at a particular time? (Or something else entirely...?) 

Posted by Richard

Anonymous said...

You know, I meant to write kiwi (which, for American undergraduates in psychology experiments, is a highly atypical bird). Unfortunately, because emus are a commonly used example in the literature, I mistakenly typed emus. I'm going to change that!

As for "within subjects disagreement," I'm sorry about that. I've been doing statistics all weekend, and I'm thinking in statistical terms. It might be better to say "intra-individual disagreement." I think I'll change that too. You interpreted it right, though. It means that if you test subjects at one time, and then give them a delay, and test them again, their definitions and categorizations will be different a significant percentage of the time. 

Posted by Chris

Anonymous said...

Chris, is this problem with Aristotelean like categories why some went to a more Sassure view of forming conferences via conceptual differences? I recall you being fairly familiar with Continental thought and wonder how you thought about that. 

Posted by Clark

Anonymous said...

Clark, I do know that Wittgenstein's critique of definitions played a role in many philosophers, on both sides of the Atlantic, turning away from definitions in general. However, I think the continental view of Aristotelian theories of concepts is formed more by a turning away from the static essentialism that you find in metaphysics from Aristotle on. When continental philosophers like Husserl, Heidegger, or Sartre talk about essences, they are referring more to individuals than to kinds, and their essences are more dynamic (subject to the processes of becoming, and to the position of perceiving subjects). The focus on difference in Heidegger, and even more in later thinkers like Deleuze and Derrida (and, though it's not really called difference, in Merleau-Ponty), seems to me like an even more radical rejection of Aristotelian essentialism, and thus Aristotilian views of definition. They seem to want to take the essence out of the thing as it is in itself and place it firmly in the dynamic structure of the lived world and language. For them, essences (if you can call them that still) are largely relational, and since the relations between things are ever-changing, so too are essences.

There is a line of thought in cognitive science that is more in line with the Continental view of Aristotelian essences than the anti-definitional accounts from people like Quine, Kripke, and Putnam in the analytic tradition. Under this view (the origin of which is usually attributed to J.J. Gibson), the structure of our concept representations is determined by our actions in the world. Objects "afford" different actions in different contexts, and this means that our concept representations will be entirely relational and context-dependent. In fact, some (including Hubert Dreyfus, on the philosophy side) believe that the context-dependence and relational nature of concepts means that they are non-representational, a view that is in line with phenomenology (at least from Sartre on) and some postmodern philosophies, especially (I would imagine) Deleuze's. You might check out Dreyfus' "A Phenomenology of Skill Acquisition as the Basis for a Merleau-Pontian Non-representationalist Cognitive Science" and Intelligence Without Representation."

Anyway, the short answer to your question is no, I don't think the same concerns about definitions that analytic philosophers detailed resulted in the anti-definition views of the continental philosophers. I think their beefs with Aristotilian views of definitions were largely metaphysical, or anti-metaphysical in nature. 

Posted by Chris

Anonymous said...

Well that was very interesting Chris. However I was more thinking of the relationship between semiotics and cognitive science. Saussure's semiotics in Europe seemed to focus on making differences and there was, to a certain extent, a similar view in Peirce. That then becomes very important to Derrida, even if Derrida arrives at it via Husserl originally. I've only made it halfway through Deleuze's Difference and Repitition. It's hard going and I ought give it an other try.

Anyway, my question was less about Analytic/Continental separations than why some cognitivists seem interested in Continental thought. I'll definitely check out Dreyfus though who I always enjoy reading. Thanks for the reference. 

Posted by Clark

Anonymous said...

Clark, sorry about that. I guess the best answer is that semiotics hasn't had much of an influence on cognitive science, outside of linguistics, and even there, the influence has primarily been in the way linguists define "signs" (in fact, they're usually just called Saussurian signs, these days). This is probably because cognitive science arose out of a computational tradition, starting with people like Chomsky, whose focus on semantics is more on the processing side than on the reference side, and therefore doesn't really deal with sign-signified relationships. In fact, one could criticize a great deal of cognitive science (including all of the major theories of concepts) for having almost no way of dealing with semantics or reference (I know that Laurene and Margolis offer this as a specific criticism of prototype theories).

I think the reason differences become important for people like Derrida and Deleuze is just that they want to avoid reifying meaning in the way that traditional Aristotelian essences or definitions do. This isn't really a concern for cognitive scientists, especially since most of them are objectivists about meaning anyway.
 

Posted by Chris

Anonymous said...

I know this isn't the point, but reading your post I thought of the following definition of bachelor and had to know what other people thought of it.

It seems to me that a bachelor is a male who is unmarried but is in the category of people who are (in the society) considered marriagable. Thus, children are not marriagable; priests are not marriagable; thus they aren't bachelors even though they are unmarried males.

The gay male question is complicated because of the historically changing nature of society. Fifty years ago, "gay male" was not a generally recognized category, and thus they were considered bachelors -- even if, with a wink, they were called "confirmed bachelors", which meant that while eligable they weren't going to be married and everyone knew it. Nowadays, however, we recongize that gay men are a category, and thus don't see them as eligible to marry women, and wouldn't consider them bachelors as such (if they were in long-term same-sex relationships many people, including me, would see them as "married", whether or not they lived in Massachusetts).

Not really trying for a mathematical-level precision here. But it seems like this is the thumbnail explanation for various objections. So please tell me:
- why this is wrong?
- what objections are not covered by this?

Thanks,

Stephen Frug

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