In common usage, the word conscience often refers to an individual’s fundamental commitment to a particular set of core moral values, that "inner voice" that guides his or her everyday decisions to act. This conception seems to reflect what people mean when they say, "I could not in good conscience do that." In this sense, one cannot act in a manner contrary to one’s conscience and preserve their moral integrity.
Theologically the term refers to a formed, rational judgment about what is right and wrong in the particular circumstances of an action. In other words, conscience is the subjective act of applying knowledge of universal moral principles to individual cases. According to the encyclical Veritatis Splendor, "[whereas] natural law discloses the objective and universal demands of the moral good, conscience is the application of the law to a particular case" [n. 59]. In this sense one can have a correct conscience, an erroneous conscience, a good conscience, a bad conscience, a morally certain conscience, or a morally uncertain conscience.
A correct conscience is one that applies moral norms to particular cases in conformity with right reason. An erroneous conscience involves making judgments that do not accord with the natural law or do not stand to reason. A good conscience means that a judgment is made to do the right thing, for the right reason, in the right circumstances. A bad conscience is reflected by the tendency to make judgments without regard for moral norms or relevant information that may affect the moral character of an action. A morally certain conscience is one in which an individual has a high degree of moral certitude concerning his or her judgment of what to do in a particular case, whereas a morally uncertain conscience is a judgment in which not enough information is available to be morally certain about that particular judgment. According to Catholic moral teaching, one has an obligation to act on a good conscience, on a morally certain conscience, and—to the extent possible—on a correct conscience.