1795 "Conscience is man's most secret core, and his sanctuary. There he is alone with God whose voice echoes in his depths" (Gaudium et Spes, par 16).
1796 Conscience is a judgment of reason by which the human person recognizes the moral quality of a concrete act.
1797 For the man who has committed evil, the verdict of his conscience remains a pledge of conversion and of hope.
1798 A well-formed conscience is upright and truthful. It formulates its judgments according to reason, in conformity with the true good willed by the wisdom of the Creator. Everyone must avail himself of the means to form his conscience.
1799 Faced with a moral choice, conscience can make either a right judgment in accordance with reason and the divine law or, on the contrary, an erroneous judgment that departs from them.
1801 Conscience can remain in ignorance or make erroneous judgments. Such ignorance and errors are not always free of guilt.
1802 The Word of God is a light for our path. We must assimilate it in faith and prayer and put it into practice. This is how moral conscience is formed.
-- From the Catechism of the Catholic Church