Terry, I completely agree with what you wrote (copy below). But I emphasized database relations because they are the most commonly used examples of relations that are defined by extension. However, the meaning of the data is specified by the rules or axioms that state the intensions. Those specifications are what we have been calling ontology. John --------------------------------------The intension / extension distinction is also crucial in the epistemology of science, insofar as the aim, goal, objective, etc. of genuinely rational scientific inquiry is to identify and express causal laws. For those laws arent merely descriptive of what actually has or is occurring in a context of precipitating conditions (as observed), but also in a cosmically nomic sense prescriptive of what would happen (under those conditions) if those conditions were met whether they actually are ever fulfilled or not. Reference class membership criteria are intensional, for instance, while the actual membership inclusion under those criteria is extensional. That intensionality of scientific language is essential for expressing the subjunctive and counterfactual nature of causation, especially for purposes not only of description (which only requires the use of extensional language), but for explanation, prediction, and corroboration as aspects of truly rational scientific methodology in general. These considerations are fairly well-covered in philosophy of science, of course, and one source I recommend is Jim Fetzers 1981 Scientific Knowledge. Im sure Susan Haack has also done important work on this, though Im at a loss for the moment as to which of her works is best to cite here. Ill look into it and report back .
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