Catechism of the Catholic Church §1734 — excerpt
Freedom makes man responsible for his acts to the extent that they are voluntary. Progress in virtue, knowledge of the good, and ascesis enhance the mastery of the will over its acts.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.