This paper considers the British thinker C.S. Lewis as a "forensic figure," defining "forensic" in the sense of public discussion and debate. The paper relates that, long before Lewis emerged as a public persuader, he learned to hold his own in private exchanges with William T. Kirkpatrick, his tutor from 1914-1917, and in letters with his Belfast neighbor, Arthur Greeves. It states that with Greeves, Lewis maintained a debate on the subject of religion--the young Lewis equated religion with mythology. The paper explains that Lewis later changed his mind about Christianity and contends that his May 11, 1959 lecture at Westcott House in Cambridge has particular merit because its claims are crucial to every defense he made of historic Christianity. After a brief overview of the talk, the paper examines in detail its content and evaluates Lewis's arguments on the basis of their clarity and soundness. According to the paper, the audience for the talk was composed mainly of seminarians, and to get across his proposition, Lewis employed a strategy that forensic educators teach early to their debaters: cast doubt on the trustworthiness and methodology of the opposition. The paper concludes that, in the Cambridge talk, Lewis demonstrated the importance of identifying basic assumptions, evaluating the evidence and reasoning behind claims, questioning terminology and definitions, understanding literary forms and various senses of meaning, and mastering biblical texts. Includes 13 notes; cites 20 works. (NKA)