|Extension, philosophy: an object, for example, the planet Venus as a material body, independent from the manner in which it is singled out. In contrast, intension is the way in which the object is given or is represented, e.g. Morning star or Evening star. See also intensions, identity, identity conditions, reference, meaning, assertibility conditions, propositional attitudes, opacity.|
|Geach, Peter T.
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Extension/Geach: E.g. to accept sense data as a more fundamental class of objects: If we know what sense data are, we can consider the extension of a predicate that is true only of sense data as identical to a particular physical object. - But this does not reduce the object itself to a logical construction. - ... + ... If there is an object like the range of z for which F(z), then x belongs to this range only if F(x).
Extension/Geach: it is a serious mistake to assume the objects formed the extension, they are only indirectly assigned to it as falling under the concept.
Theory/extensional/Geach: no theory, no matter how rich, may contain all classes which are the extensions of their own sentences. - (> semantic paradoxes).
Logic Matters Oxford 1972