Isomorphism-inspired theorising about optionality and variation: no empirical support from English grammar

Abstract Language variation (specifically: optionality between different ways of saying the same thing, as in check out the places vs check the places out ) tends to be considered abnormal, suboptimal, short-lived, dysfunctional and needlessly complex, especially in functional or cognitive linguistic circles. In this contribution, we are assessing these assumptions: does grammatical optionality increase the relative complexity (or: difficulty) of language production? We use a corpus-based psycholinguistics research design with a variationist twist and analyse SWITCHBOARD, a corpus of conversational spoken American English. We ask if and how grammatical optionality correlates with two symptoms of production difficulty, namely filled pauses ( um and uh ) and unfilled pauses (speech planning time). Our dataset covers 108,487 conversational turns in SWITCHBOARD, 22 grammatical alternation types yielding 57,032 optionality contexts, 589,124 unfilled pauses and 43,801 filled pauses. Analysis shows that overall optionality contexts do not make speech production more dysfluent – regardless of how many language-internal probabilistic constraints are in operation, or how many variants there are to choose from. With that being said, we show how some alternations in the grammar of English are more prone to attract or repel production difficulties than others. All told, our results call into question old dogmas in theoretical linguistics, such as the Principle of Isomorphism or the Principle of No Synonymy.