This chapter discusses the picture theory of meaning, elementary objects and elementary names, ostension, isomorphism, showing, sense, logical form, what can be said, logical space and truth-tables, tautology and positivism. It also discusses verifiability criterion, behaviorism and methodological behaviorism, operational definition, eliminative materialism, cognitive psychology and cognitive science, the computational model and artificial intelligence and Turing test. Behaviorism lost its dominant position in psychology in the United States during the 1950s and 1960s in large part because its proponents dogmatically insisted that mental states and processes could not be investigated scientifically. The fundamental idea of cognitive psychology is that cognitive processes can be modeled by developing abstract, formal 'representations' of cognitive processes. In the 1920s Ludwig Josef Johann Wittgenstein began to lose faith in the doctrines of the Tractatus on at least three grounds - each of which has implications for cognitive psychology, cognitive science and the computational model of cognition.