Catechism of the Catholic Church §1758 — excerpt
The object chosen morally specifies the act of willing accordingly as reason recognizes and judges it good or evil.
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.