In defending a statement by John (Cardinal) Newman about the supremacy of conscience over authority, John Paul II wrote  “If a man is admonished by his conscience – even an erroneous conscience, but one whose voice appears to him as unquestioningly true – he must always listen to it. What is not permissible is that he culpably indulge in error without trying to reach the truth. If [Cardinal] Newman places conscience above authority he is not proclaiming anything new with respect to the constant teaching of the Church. The conscience, as the [Second Vatican] Council teaches, 'is man's sanctuary and most secret core, where he finds himself alone with God, whose voice resounds within him.' "   

In his book, John Paul II explains that the supremacy of conscience has been the Church’s teaching from the beginning and “echoes the teaching of the Fathers and the theological tradition from Saint Thomas Aquinas to John Henry Newman.”