In the context of his experiences in groups, Bion (1950c [1961]) coined an unusual term for a rather unfamiliar idea. The term was proto-mental, and the idea was that of a system or matrix where physical and mental were undifferentiated; he postulated that this proto-mental matrix was the source of basic pre-verbal emotions. From this proto-mental source, basic emotions could evolve and lead to primitive group-as-whole emotional field phenomena which he called basic assumption groups, or just basic groups. Additionally, if proto-mental phenomena were confined in a latent phase in the proto-mental matrix, they would manifest in certain symptoms with undifferentiated physical and mental components. Finally, he stated that the sphere of protomental events could not be understood by reference to the individual alone, for proto-mental phenomena are a function of the group. Although Bion did not use the term proto-mental after 1961,1 the notion of indistinct physical and mental components of sense impressions of emotional experiences was maintained throughout all his later writings, namely in his concept of A-elements.2