Processing, Prosody, and Optional to

The infinitival marker to is optional in many instances of the do-be construction, exemplified by sentences like All I want to do is (to) go to work However, it has not previously been investigated what factors govern speakers’ choices in to use and omission. Here, we analyze nearly 10,000 such examples from the Corpus of Contemporary American English (COCA), using mixed-effects logistic regression to determine the respective contributions of a range of factors including phrasal complexity, wordform frequency and predictability, and prosody in predicting to use. We found that to use rate increases as phrasal complexity increases and as wordform frequency and predictability decrease, consistent with established psycholinguistic theory and data on the use of other optional function words. We also find the first quantitative corpus-based evidence for a role of prosody in governing optional function-word use: to is used more frequently when both the immediately preceding and the immediately following syllables carry some stress. This suggests that speakers use the intervening unstressed to to prevent stress clash. This result holds in writing as well as in speech, lending support to Janet Fodor’s proposal that implicit prosody plays a role in sentence processing.