This conclusion presents some closing thoughts on the concepts discussed in the preceding chapters of this book. A monograph contributes to the development of theories of motivation by subjecting some leading examples of contemporary theories to conceptual analysis. Conceptual confusion is one of the main causes of the present unsatisfactory state in motivational psychology. In theories of motivation, in addition to purposive rule-following explanations, and those in terms of efficient causes, there are also to be found all-inclusive explanations in terms of concepts like 'need reduction', 'homeostasis', 'satisfaction', and so on. Hedonism, which has been recently revived, is a case in point. Psychology has not soared into its Galilean period as is often thought, through lack of bright ideas, experimental ingenuity, or methodological rigour. Ambitious theories of motivation tend to take models of explanation that are appropriate to answering some forms of 'why' questions and to generalize them to answer quite different forms.