ABSTRACT
Philosophers have concluded that our thoughts are proof that we exist: Cogito ergo sum (I think, therefore I exist). Psychologists, however, take this one step further: The nature of our thoughts reveals the level of development at which we exist (e.g., Piaget, 1937; Rapaport, 1951; Werner, 1940). Over the course of expectable development, a child’s thought will evolve from primitive sensorimotor processes to more sophisticated reversible operations. The primary process becomes subordinated to the secondary process. Thought becomes less concrete; abstraction and symbol deployment become possible. Inner and outer are untangled, each increasingly differentiated and articulated: Concepts and percepts become incrementally separate and accurate. Ideas that once dominated and controlled the mind become tentative hypotheses, testing internal and external worlds. Adaptation is served by the progressive evolution and maturation of thinking (Hartmann, 1939).
