Tuesday, July 27, 2010

Ontology and Concepts

Ontologies describe concepts, concepts humans form in their heads of real things - physical or abstract - which exist outside of their heads. Concepts are more or less detailed, as the circumstances require; the real (outside) things are always fully determined: there is no dog without a definite fur color or gender - but a concept of a dog a friend talks about may remain of unspecific color or gender, as long this is not relevant for the story he is telling.
We construct concepts in reaction to outside stimuli - something we see or a word we hear. Concepts are in a state. If a conversation continues, the concept becomes more specific; for example, the hair color of the dog may become mentioned.
Rosch has pointed out, that concepts are not fixed sets of things, but have a radial (graded) structure: some exemplars are better examples than others. Robins are "better birds" than penguins or ostriches. The structure of a radial category may change under the influence of a context: if the discussion focuses on Antarctica, penguins become "better" examples of birds.
How to model concepts and the effects of contexts on them? Consider additional information as a piece of context, which changes the state of the concept. Aerts and Gabora in "A theory of concepts and their combination" (2005) suggest that quantum mechanics provides a framework to model the state of concepts and the action of context on the state of the concept.
I have constructed concrete models of the concept "pet", following the experimental data they report in the paper. Starting with a little determined state of the concept "pet", where the pet can be a dog, a cat, a goldfish, additional context, e.e. a statement "the pet is running in the garden", makes the state of the concept more determined: goldfish is excluded, dog or cat becomes more likely. The formal model does identify absurd combinations of contexts, e.g. "the pet runs in the garden" and "the pet is a fish" - humans in conversation will in this moment ask for clarification...

What have I learned? The confusion between concepts and things in reality is difficult to avoid - we have a natural tendency to talk about the things, but meaning the concepts. Accepting that concepts have states makes the ontology enterprise much more difficult: when we give the ontology of a concept, which state are we describing?

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