Piaget's central tenet in this volume is to illustrate that children's realism, animism, and artificialism are the results of children's attribution of their thoughts, desires, and imaginations to the external world. The failure to draw a boundary between the self and the external world results in a fusion of the two. As such, realism emerges as chil- dren's inability to distinguish internal from external and the sign from the signified. This is evident in his inter- views with children on psychological phenomena such as thought, words, and dreams. According to Piaget, rea- lism is transformed through stages moving from identifying the psycho- logical and physical phenomena as one to understanding them as separate.