With the new millennium, papal power sought to restore Christian rule in the Holy Land through a series of eight crusades, but these campaigns were military and political failures, especially at the expense of the Papacy. However, they did succeed in opening the way for the scholarship of the Islamic world to enter western European intellectual life. With the founding of universities, new scholarship slowly emerged. The pioneering teachings of Pierre Abélard, Roger Bacon, and Albertus Magnus led to a revival of interest in the ancient writers with their emphasis on rational thought to secure human knowledge. This movement, called Scholasticism, reached its pinnacle with the writings of St. Thomas Aquinas who sought a reconciliation of Aristotle’s rationalism and Christian theology. A major implication of Aquinas’ success was the acceptance by scholars within the universities and the Church that both reason and faith serve as sources of human knowledge. William of Ockham extended the Scholastic movement and his predecessor Roger Bacon by presented a law of parsimony in scientific explanation, which in turn laid the foundation of empirical science.

On a cultural level, the Italian Renaissance lifted Europe into a new era of humanism that glorified humanity and shifted attention to the present needs and desires of people. Erasmus translated this humanistic attitude into scholarly pursuits that revealed the frailties and needs of the human authors of Scripture. All of these forces eroded the authority of the Church, leading to dramatic confrontation, both from inside and outside the Church. The Protestant Reformation took advantage of the rift between Christian monarchs and the papacy, successfully fragmenting the unity of Western Christendom. However, it was Copernicus who used the strategy and tools of reasoned arguments to arrive at his heliocentric theory of planetary motion. This bold assertion successfully demonstrated a truth arrived at through reason that differed from the conclusion supported by the authority of the Church. As a result, reason triumphed over faith, and the age of science began. While psychology remained obscured within philosophy and religion during this time, the enduring questions still perplexed scholars and were about to be addressed directly over two centuries of philosophical inquiries prior to psychology’s formal definition as a distinct science.

The scope of this book is summarized in terms of the basic issues that have historically confronted psychology. The five systems of psychology -- psychoanalysis, Gestalt psychology, the third force movement, behaviorism, and cognitive psychology -- have been compared along critical areas of neo-functional applications and extensions of psychology as well as the enduring questions. The result points to the relationship between psychology and science, and in particular, the problems resulting from a reliance on materialistic empiricism. Psychology as a theoretical discipline has suffered from the disagreements and controversies since its formal definition in the 1870s. Yet during this time, psychology has been successful as an applied science.

The process of entities successively splitting into two or more is of great relevance: biological reproduction, infection spreading, rumour spreading, nuclear reactions and much more.

Emergent phenomena require some interdependence between components. Networks of nodes and connecting links are therefore a very natural and powerful language for the analysis and characterisation of complex systems.

The psychoanalytic movement introduced the study of unconscious processes that influence human activity. The movement was fully consistent with the German model of mental activity, going back to the writings of Leibniz and Kant. Although act psychology and the Gestalt movement were also modern expressions of the German model, psychoanalysis emphasized the goal of a homeostatic balance of unconscious energies within personality. Its founder, Sigmund Freud, used his keen powers of observation to devise much-needed therapeutic approaches, and later expanded his formulations to a psychodynamic theory of personality growth dependent on tension reduction. Other theorists modified Freud’s model to include cultural influences (Jung) and social needs (Adler and Horney). In addition, scholars have integrated the psychoanalytic model with a field approach (Sullivan) and existential assumptions (Fromm). As a contemporary movement, psychoanalysis still exerts considerable influence in psychiatry and clinical psychology, although the movement is fragmented owing to a lack of methodological agreement. In addition, Freud’s statements on the unconscious have led to new interpretations of artistic expression. However, as a viable model for psychology, psychoanalysis has departed from the empirical foundations of psychology and shares little with other systems of psychology that rely on that methodological approach.

Behavioral psychology was immediately preceded by the reflexology of Russian physiology and the associationism of Thorndike. Physiological reflexology received a sound foundation with the works of Sechenov and Bekhterev, but it was Pavlov who proposed a comprehensive theory of conditioning. Watson’s behavioral formulation defined stimulus and response elements as the substitute to rid psychology of residual mentalistic constructs. Watson’s contemporaries, Holt, Weiss, Hunter, and Lashley, soon restored to behaviorism critical psychological activities. The logical positivist movement expressed an operational spirit and insured the initial success of the behaviorist model. Behavioral psychology expanded beyond the original formulations of Pavlov and Watson. Contemporary reflexology in Russia and in nearby countries expanded to include a wide range of psychological and physiological problems, led by such eminent scientists as Vygotsky, Luria, Konorski, Asratyan, and Beritashvili. In the United States, behaviorism moved through several intellectual stages, through the contributions of Guthrie, Tolman, Hull, and Skinner. A major application of behaviorism was the behavior modification model in clinical settings. Contemporary behaviorism remains a dominant but diffused force in psychology.