letting "a foolish maid" convince a child that "goblins and sprites" are associated with the night for "darkness shall ever afterwards bring with it those frightful ideas, and they shall be so joined, that he can no more bear the one than the other." "Associationism", as this theory would come to be called, exerted a powerful influence over eighteenth-century thought, particularly educational theory, as nearly every educational writer warned parents not to allow their children to develop negative associations. It also led to the development of psychology and other new disciplines with David Hartley's attempt to discover a biological mechanism for associationism in his Observations on Man (1749). Jean-Jacques Rousseau Jean-Jacques Rousseau, though he paid his respects to Plato's philosophy, rejected it as impractical due to the decayed state of society. Rousseau also had a different theory of human development; where Plato held that people are born with skills appropriate to different castes (though he did not regard these skills as being inherited), Rousseau held that there was one developmental process common to all humans. This was an intrinsic, natural process, of which the primary behavioral manifestation was curiosity. This differed from Locke's 'tabula rasa' in that it was an active process deriving from the child's nature, which drove the child to learn and adapt to its surroundings. Rousseau wrote in his book Emile that all children are perfectly designed organisms, ready to learn from their surroundings so as to grow into virtuous adults, but due to the malign influence of corrupt society, they often fail to do so. Rousseau advocated an educational method which consisted of removing the child from society—for example, to a country home—and alternately conditioning him through changes to his environment and setting traps and puzzles for him to solve or overcome. Rousseau was unusual in that he recognized and addressed the potential of a problem of legitimation for teaching. He advocated that adults always be truthful with children, and in particular that they never hide the fact that the basis for their authority in teaching was purely one of physical coercion: "I'm bigger than you." Once children reached the age of reason, at about 12, they would be engaged as free individuals in the ongoing process of their own. He once said that a child should grow up without adult interference and that the child must be guided to suffer from the experience of the