A modal ambiguity in for-infinitival relative clauses

This squib presents two puzzles related to an ambiguity found in For-infinitival relative clauses (FIRs). FIR’s always receive a modal interpretation even in the absence of any overt modal verb, and the modal interpretation seems to come in two distinct types, which can be paraphrased by finite relative clauses employing, respectively, the modal auxiliaries should and could. The two puzzles presented here concern the compositional analysis of FIRs. Both puzzles arise from the fact that the availability of the two readings is constrained by factors that are not otherwise known to affect the interpretation of a relative clause. Specifically, we show, first, that “strong” determiners require the FIR to be interpreted as a SHOULD-relative while “weak” determiners allow both interpretations (the Determiner-Modal Generalization). Secondly, we observe that the COULD-interpretation requires a raising (internally headed) structure for the FIR, while the SHOULD-interpretation is compatible with either a raising or a more standard matching (externally headed) structure (the Raising/Matching Generalization).