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of Philosophy. This thesis describes a theory of relation changing rules In LFG, concentrating on rules which distinguish between unaccusative and unergative verbs. I call these rules Unaccusative Rules (URs). In order to handle URs I introduce a new mechanism which I call Argument Classification (AC) which mediates betwe\3n thematic roles and grammatical functions, AC puts thematic arguments into one of four argument classes: unexpressed, semantically restricted, subjective unrestricted, and general unrestricted. Then, grammatical functions are assigned to these classified arguments instead of being assigned to unprocessed thf:matic argument slota, The theory of relation changing rules specifies allowable argument classifications and allowable assignments of functions to classified arguments, In order to illustrate the theory. I formulate a number of rules in English and Dutch. Chapter 1 p"ovides background information about grammatical relations and relation char~ging rules in LFG, Chapter 2 summarizes properties of relation changing rules which a theory should account for: semantic conditioning, syntactic productivity, ability to distinguis