Some Catholic scholars, such as Jesuits Peter Fink and George T. Dennis of Catholic University of America, have argued that we cannot know if priests in early Christianity practised sexual abstinence. Dennis says "there is simply no clear evidence of a general tradition or practice, much less of an obligation, of priestly celibacy-continence before the beginning of the fourth century." Fink says that a primary book used to support apostolic origins of priestly celibacy "remains a work of interpretation. There are underlying premises that seem to hold firm in this book but which would not stand up so comfortably to historical scrutiny."