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Reactions to Darden Editor: We are sympathetic to Lindley Darden's intellectual program. But the various conceptions of abstraction which she discusses are, individually and collectively, inadequate. There are two problems, one concerning the basic nature of abstraction and the other concerning a mechanism by which abstract terms can be related to their definitional base. Darden comes close to the basic nature of abstraction when she asserts that "In difficult cases, forming an abstraction can involve more than merely dropping parts or replacing constants with variables. New, abstract semantic concepts might have to be introduced."