Lewis raises two questions: whether serving in war is morally bad, morally indifferent, or morally obligatory, and, more generally, how to decide what is good or evil.

The usual answer to the second question is that one decides based on one’s conscience. However, Lewis posits that conscience is persuadable and, as such, is not a separate faculty but rather the whole person engaged in a moral question. Further, conscience can be understood in two senses: either as an inner voice telling the individual to do what is right or as the specific judgment about the content of right and wrong. Conscience in the first sense “is always to be followed” (65), but conscience in the second sense can be mistaken.

There is a parallel between conscience and reason, which consists of the act of judging between truth and falsehood. The act of reason begins with the reception of facts, which may come from either experience or authority. Once the facts are understood, reason performs a “simple act” of perception, known as intuition. Third, reason arranges various facts to yield a series of such intuitions. Rational intuition cannot be produced by argument or persuasion; either one has it, or one doesn’t.