There remains some confusion on the matter among both Catholics and non-Catholics. This confusion can be seen in those who interpret Catholic researcher James Keenan to claim that the doctrines given by apostolic tradition have changed. Keenan reviewed the history of moral theology, and in particular a change in the approach of moral theologians, specifically in the twentieth century. Keenan noted that Mark D. Jordan said that medieval texts he had reviewed appeared to be inconsistent. This refers to medieval traditions and not to apostolic tradition or doctrine. Keenan, however, says that John T. Noonan Jr. demonstrated that, "despite claims to the contrary, manualists were co-operators in the necessary historical development of the moral tradition". According to Noonan, "history cannot leave a principle or a teaching untouched; every application to a situation affects our understanding of the principle itself."