20 It is worthy of note how a layman, an excellent writer and at the same time a profound and conscientious thinker, has been able to understand well and express exactly this fundamental Catholic doctrine: The Church does not say that morality belongs purely, in the sense of exclusively, to her; but that it belongs wholly to her. She has never maintained that outside her fold and apart from her teaching, man cannot arrive at any moral truth; she has on the contrary more than once condemned this opinion because it has appeared under more forms than one. She does however say, has said, and will ever say, that because of her institution by Jesus Christ, because of the Holy Ghost sent her in His name by the Father, she alone possesses what she has had immediately from God and can never lose, the whole of moral truth, omnem veritatem , in which all individual moral truths are included, as well those which man may learn by the help of reason, as those which form part of revelation or which may be deduced from it.
Source: Divini Illius Magistri (Vatican.va)