Originally the term psychic structure was not defined clearly, and subsequently it acquired various different meanings. This paper illustrates that Freud's carryover of his concepts of psychic energy from the libido theory of his topographic model into the tripartite model has been an important source of confusion about the meaning of the term structure. Reification and concretization have also added to misunderstandings of structure. The usual definitions of structure tend to include the functional, organizational, and stability dimensions of structure, but there has been insufficient recognition of the development and functional interrelatedness of the id, ego, and superego. There are important differences in the tripartite model of 1923 and modern structural theory which affect our understanding of the nature of structural change during psychoanalytic treatment. Misunderstandings about the definition of structure have also contributed to perpetuating the spurious dichotomous contrast of pathogenesi due to failures in structural differentiation and pathogenesis due to conflict.