This chapter discusses the nature of philosophy, causal concepts, the nature of science as classifying and explaining, needs of a scientific psychology, positivism, empiricism, ontology, Cartesians, behaviorism, cognitivism, causal and normative explanations, discursive and cultural psychology. Positivism was both a cluster of philosophical claims about the scope and possibilities of obtaining knowledge and an attitude toward the place of human beings in the world. Ludwig Josef Johann Wittgenstein was a leading figure in developing several very different accounts of what symbols mean, and consequently of what the basis of thinking might be. His first attempt was based on the presupposition that all words, except those expressing grammatical structure, are names. A new era in psychology has arrived in many places, influenced to a considerable extent by the critical insights offered by Wittgenstein and others who have drawn encouragement and inspiration from his writings.