This paper challenges the view that mental contents can be innate and offers instead a developmental model in which mental contents emerge from the interaction of genes, brain and environment. Some key steps on this developmental pathway are traced, such as the formation of image schemas. The processes by which mental contents are evaluated and organized are described, notably those of perceptual analysis, representational re-description and appraisal. Jung's concept of the transcendent function is seen to have certain crucial features in common with each of these processes. The emergence of the capacity to symbolize is explored in relation to these concepts and it is suggested that the pinnacle of this capacity is achieved in the emergence of reflective function, in which mind is represented to itself.