The Role of Frequency and Optionality in the Regularization of Linguistic Variation

Languages are widely known to become more regular over time, yet not all variation is regularized — some forms resist regularization and remain stable over many generations. A large body of work has explored why learners regularize unpredictable variation, often focusing on the cognitive mechanisms that underlie this behavior and how these mechanisms differ between adults and children. However, less attention has been given to investigating the factors that allow some variation to remain stable over time. In this paper, we propose that optionality may be a particularly stable form of linguistic variation, likely to resist cognitive pressures to regularize. To test this hypothesis, we conducted two artificial language learning experiments designed to investigate the conditions under which optionality remains stable or becomes regularized. In Experiment 1, we compared optional variation to variation involving two alternating overt forms, expecting optionality to show greater stability. In Experiment 2, we explored whether the frequency of the optional form would influence regularization, hypothesizing that rare optional forms might resist regularization more effectively than frequent ones. Our findings suggest that, while optionality is not inherently more stable, it is nonetheless special, revealing critical insights into cognitive mechanisms proposed to be responsible for regularization behavior in child and adult learners.