This text traces the Latin scholastics’ attempt to deal with two essentially incompatible notions of the human soul: the scientific view of Aristotle which considers it to be a form; and the Augustinian view of the soul as a substance in its own right. It traces the growing disarray of Latin notions of the soul, the growth of the monopsychism controversy and the solutions of Bonaventure and Aquinas through the variety of responses to Aquinas’s De unitate intellectus . Among its conclusions are that the traditional dualism diminished with time, that there was little agreement among the heterodox Aristotelians and that, with two exceptions, no one in the 13th century taught the present position of the Catholic church, namely that the rational soul is infused at conception.