Starting with the observation that focus phrases can be dichotomized on the basis of whether they are exhaustive or not, this paper shows that exhaustive focus triggers intervention effects for wh-in-situ argument questions, while non-exhaustive focus does not. Empirical data from typologically unrelated languages are cited to support this generalization; exceptional cases are argued to arise on independent grounds. No existing analysis of intervention effects takes into consideration the distinguished behaviors of exhaustive and non-exhaustive focus in terms of triggering intervention effects for wh-in-situ argument questions. I argue that with some modifications, the semantic approach which draws on the interpretation similarity between focus phrases and wh-phrases constitutes the most promising analysis. Intervention effects arise when the focus operator associated with exhaustive focus phrases unselectively evaluates both the focus semantic value and exhaustivity of the in-situ argument wh-phrase in its scope.
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