I. Notion

The notion of moral theology - as the notion of every science - must be drawn from its object. For since knowing is an action or direction of the mind, and every action is directed by its object, it follows that any science whatever is defined from the notion of its object. Considering these things, moral theology can be defined: the science which teaches, from supernatural principles, what is commanded or forbidden in order to the ultimate supernatural end. It is said:

1. What, or what human actions are commanded or forbidden. By these words the material object of moral theology is indicated. Human actions constitute it, and indeed those actions which fall under command or prohibition. Namely, moral theology, strictly speaking, generally teaches how man is directed to the ultimate end. But lest its matter grow out beyond measure, it does not dwell on each individual act of the Christian life; rather, content with narrower limits, it regards those things, at least chiefly, which are imposed or forbidden by law or precept.

2. In order to the ultimate supernatural end. By these words the formal object which of moral theology is assigned. Human actions constitute it insofar as they are commanded or forbidden in order to the ultimate supernatural end.

3. From supernatural principles. By these words the formal object by which of moral theology is indicated. That is, the said science draws its knowledge of commanded or forbidden human actions from principles taught by God immediately or mediately. Yet in the course of the treatises we shall not pass over principles founded upon natural reason, as will appear more clearly from the sources to be assigned under II.

From what has been said it is gathered that moral theology differs: 1. from dogmatic theology, which regards speculative truths more, while moral theology dwells on practical matters. Yet both constitute one science, which is called theology; 2. from ascetical theology and mystical theology, which regard those things that are not commanded but are supererogatory and pertain to the perfection of the Christian life;¹ 3. from canon law, which treats human actions insofar as they are directly ordered to the common good of the Church; 4. from moral philosophy, which, founded on principles known by the natural light of reason, considers human actions in order to the natural end.

¹ Moral theology, as we have said, by force of the term certainly comprehends all morals or human actions; but lest its matter be extended too far, it regards only those things which, by the law of God, fall under command or prohibition. The rest are left to ascetical theology or mystical theology, according as the discussion concerns the ordinary way or the more or less extraordinary way.

As regards St. Alphonsus, he is not only Doctor of moral theology, but also of ascetical and mystical theology. His spiritual works contain ascetical theology, not indeed written systematically, but nevertheless written with great wisdom and abundance of matter. In them the chief point is the doctrine concerning loving and imitating Jesus Christ, concerning constancy in praying, concerning invoking the Blessed Virgin Mary, and concerning the method of meditating. You will find mystical theology concisely and briefly, yet almost completely, in the Praxis Confessarii, which is at the end of the Theologia Moralis, chapter VII and especially chapter IX.