Now it is almost taken for granted by many psychologists that a cognitive theory should be like a computer program. But we know that cognitive science is the science of mind. Therefore cognitive scientists seek to understand perceiving, thinking, remembering, understanding language, learning and other mental phenomenon. Their research is remarkably diverse, ranging from observing children’s mental operation, through programming computers to do complex problem solving, to analyze the nature of meaning. In order to appreciate the work in artificial intelligence, which is a necessary part of cognitive science, it is necessary to have some familiarity with theories of human intelligence. The cognitive scientists introduce the notion of machine intelligence and emphasize the relationship between human and machine intelligence. The aim of artificial intelligence is to develop and test computer programs that exhibit characteristic of human intelligence. The most fundamental contribution of symbolic computational modeling has been the physical symbol system hypothesis. According to Newell and Simon, “a physical symbol system has the necessary and sufficient means for general intelligent action,”¹³ By ‘necessary’ we mean that any system that exhibits general intelligence will prove upon analysis to be a physical symbol system. By ‘sufficient’ we mean that any physical symbol system of sufficient size can be organized further to exhibit general intelligence. Lastly, by ‘general intelligent action’ we wish to indicate the same scope of intelligence as we see in human action; that in any real situation behaviour appropriate to the events of the system and adaptive to the demands of the environment can occur within some limits.