Directional forces in the evolution of grammar

Languages have diverse characteristics that have emerged through evolution. In modern English grammar, the perfect is formed with have+PP (past participle), but in older English the be+PP form existed as well. It is widely recognised that the auxiliary verb BE was replaced by HAVE throughout evolution, except in several exceptional cases. However, prior studies have not clarified the evolutionary factors behind this phenomenon. In this study, we combined three large-scale corpora of English (Early English Books Online, Corpora of Historical American English, and Google Books) and analysed them to illuminate the factors that drove the evolution of the perfect in English. Our results provide important insights into the evolution of grammar. We found that most intransitive verbs exhibited an increase in the frequency of have+PP, some of which passed the Frequency Increment Test (FIT), indicating a rapid S-shape increase. This finding strongly suggests that the perfect could have evolved through natural selection rather than random drift.