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Classes/Art/intensional view/Arndt: e.g. Aristotle: Form, Entity - also Locke: in his view nominal essence - on the other hand extensional perspective: (also Locke): here type of a complex idea, whose name can be applied to a scope (extension),which the idea of the type specifies. - Similarity: results from compliance with our idea of the type - similarity: we must assume that there is something equivalent in nature, without that we can say something about their real quality.
An Essay Concerning Human Understanding