Ruth Jackson speaks with Lilian Lindén about CS Lewis’ early philosophical development and his long-running debate with his friend Owen Barfield, the so-called “Great War.” They unpack Lewis’s shift from realism to idealism, explore Barfield’s influence through anthroposophy, and consider how figures like Rudolf Steiner shaped their discussions. The conversation also looks at Lewis’ rejection of materialism, why these philosophical questions still matter, and how his early intellectual battles continue to speak into today’s sceptical and materialist culture.