ABSTRACT
If the mental life of the civilized man were the only form of mental life presented for our contemplation, we might well despair of obtaining any useful understanding of it. For long ages the philosophers who concerned themselves with the mental life fixed their attention almost exclusively on the civilized adult: it was largely for this reason that, while other sciences were rapidly extending man’s mastery over the physical world, psychology remained rudimentary and ineffective. Descartes, the most influential thinker of the opening years of the modern period, accentuated this tendency to set apart the mental life of man from all other fields of scientific inquiry, to separate psychology from biology: for he taught that animals are merely complex mechanisms without mental life, and that man is a similar mechanism to which is attached a mind, soul, or thinking thing, res cogitans.
