This book is the first place Steiner mentions the threefold mapping of human thinking, feeling, and willing onto the nervous and sensory system, the rhythmic system, and the metabolic/limb system. This tripartition then becomes central to Steiner's later development of Waldorf education and the so-called Threefold Social Order. It also features a long obituary celebrating Franz Brentano, who was Steiner's teacher and a co-founder of the phenomenological movement in philosophy.