SUMMARY This is an attempt to formulate the nature of the sacraments in relation to the Church, to the deposit of faith, and to church order, in order to try to establish a way of viewing sacramental practice in terms more positive than validity and invalidity, which now loom uncomfortably large over ecumenical relationships. Part I, dealing with three preliminary questions, first gives a survey of the pronouncements of the Church on the invalidity of Protestant sacraments; added to the defectus intentionis the Church denounces in the Protestant ministry a lack of competence to administer the sacraments after Baptism, even in the case of the Anglican Church, which claims a valid ministry. After this it is laid down that whereas the concept of (in)validity is only prominent in paradoxical situations (especially those in which mala fides plays a part), traditional theology has formulated the nature of the sacrament almost exclusively in terms of (in)validity, thus basing itself on a marginal concept of the ...