This paper presents a comparison of two psychoanalytic models of how human beings learn to use their mental capacities to know meaningfully about the world. The first, Fonagy's model of mentalization, is concerned with the development of a self capable of reflecting upon its own and others' mental states, based on feelings, thoughts, intentions, and desires. The other, Bion's model of thinking, is about the way thoughts are dealt with by babies, facilitating the construction of a thinking apparatus within a framework of primitive ways of communication between mother and baby. The theories are compared along three axes: (a) an axis of the theoretical and philosophical backgrounds of the models; (b) an axis of the kind of evidence that supports them; and (c) the third axis of the technical implications of the ideas of each model. It is concluded that, although the models belong to different theoretical and epistemological traditions and are supported by different sorts of evidence, they may be located along the same developmental line using an intersubjective framework that maintains tension between the intersubjective and the intrapsychic domains of the mind. Copyright 2007 by The Spanish Journal of Psychology.