Robert Halifax, a brilliant Oxford Calculator, developed a seminal concept of the will that influenced late medieval philosophy and theology. The critical edition of question 5 from Halifax’s Questions on the Sentences, offered in this volume, facilitates further research on his contribution to voluntarist debates. It illuminates the way Halifax marshalled the measurement language and analytical tools to anatomize the will and its acts, enabling him to craft a unique framework for the study and description of the will that resonated with Calculatory ethics. It was a novel methodological and doctrinal approach embraced by Oxonians at that time.