Interpreting Disjunction under Deontic Modals: An Experimental Investigation

Abstract

Disjunction under a deontic possibility modal (i.e., may/or sentences) or a deontic necessity modal (i.e., must/or sentences) may give rise to three types of inferences: free choice inferences (i.e., the inferences which imply that the options indicated by each of the individual disjuncts are permitted), exhaustivity inferences (i.e., the inferences which imply that the options that are not indicated by the individual disjuncts are not permitted), and exclusive or inferences (i.e., the inferences which imply that no more than one option indicated by the individual disjuncts is permitted at the same time). There is an ongoing debate among recent theoretical studies (e.g. Fox, 2007; Geurts, 2005; Simons, 2004) regarding whether these inferences are available and how they are derived for each of the above mentioned constructions. In experiments, the availability of the inferences can be reflected by derivation rates, while the derivation mechanism of the inferences can be reflected by processing time-courses. Based on this, an experiment involved with a picture-sentence binary judgment task was conducted in this study. It examined the the derivation rates and processing time-courses of the three types of inferences drawn from may/or sentences and must/or sentences. The results of the experiment indicate that in the processing of may/or sentences and must/or sentences, free choice inferences were similarly derived around 90% of the times, and the derivation of them was not accompanied by an increase of processing time (i.e., the derivation of them did not take a longer time than the derivation of logical meanings). The results further indicate that exhaustivity inferences and exclusive or inferences were derived around 15% and 30% of the times for may/or sentences respectively, and the derivation of them was accompanied by an increase of processing time. Compared with this, exhaustivity inferences and exclusive or inferences were derived around 98% and 94% of the times for must/or sentences respectively, and the derivation of them was not accompanied by additional processing time. It seems that under the current experimental paradigm, may/or sentences were interpreted as expressions that grant weak permission, while must/or sentences were interpreted as expressions that grant strong permission. The results seem to be consistent with Simons’s (2004) account to a large extent.