Mere Marriage: Sexual Difference and Christian Doctrine proposes that Pope Saint John Paul II's radical theological teaching on the meaning of sexual difference heralds a development of Christian doctrine. In an age that accords little significance to sexual difference, John Paul follows Henri de Lubac's advice: "When something so fundamental] is called into question you have to get down to its roots...the whole matter has to be studied from a new viewpoint. Fundamentally, what you feel is a need to see straight." Mere Marriage highlights sacred tradition, by presenting Church Fathers, Medieval and Modern theologians, and also presents natural law and personalism which apply different methods and reach diverse conclusions. Mere Marriage then compares Humanae Vitae and the Theology of the Body as disparate treatises on conjugal love and shows that the latter's personalistic conclusions assimilate and develop the former's natuarisistic conclusions. Then it applies Saint John Henry Newman's seven tests of genuine doctrinal developments to the Theology of the Body's personalistic conclusions and shows that Newman's tests do not disqualify John Paul's proposal as a potential genuine development of Christian doctrine.