In about 1958, Merleau-Ponty told Sartre that he would write a book on nature. The news does not seem to have surprised Sartre, but one wonders why it didn't. After all, Merleau-Ponty had already had his say on this issue: both The Structure of Behavior and Phenomenology of Perception, his first two books and certainly his best known efforts, make up a single prolonged study of the relationship of consciousness and nature. It concludes to that philosophical primacy of the union of these in perception which has been Merleau-Ponty's “trademark” ever since. It was completed by 1945. Shortly afterward, he promised that he would describe the passage from perception to explicit, conceptualized knowledge in a book which he would call l'Origine de la Vérité. Meanwhile, he turned from the relations of consciousness with nature to those of consciousness with consciousness and worked at a phenomenology of history (in the period, roughly, from 1945 to 1955), a phenomenology of language (from 1950 to 1953), and even a phenomenology of philosophy (from 1953 to 1956).