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.

Research in judgment and decision making has made a lot of progress on the front of the identification of biases, and, more recently, on their correction, by suggesting feasible interventions to reduce their prevalence. Despite initial mixed results, more recent research has revealed that training is a promising debiasing tool. One-shot training interventions can reduce the incidence of several cognitive biases up to three months post training. These effects generalize to decisions and problems that were not featured in the training but are susceptible to the same biases. They were also observed in a field setting when trainees were not able to connect the decision problems to the training. Although the complexity of the decision strategies taught and the propensity of trainees to see themselves as immune to bias may pose boundary conditions to the occurrence of these effects, training has notable advantages in comparison to other debiasing tools such as incentives, accountability, and nudges.

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 empirical study of belief is emerging at a rapid clip, uniting work from all corners of cognitive science. Reliance on belief in understanding and predicting behavior is widespread. Examples can be found, inter alia, in the placebo effect, attribution theory, theory of mind, and comparative psychological literatures. Research on belief also provides evidence for robust generalizations, including about how we fix, store, and change our beliefs. This article provides the first detailing of the psychofunctionalist account of belief. The picture of belief that emerges is one where belief fixation is automatic and effortless, and independent of controlled and effortful belief rejection. Belief is then stored in fragmented networks of causally isolated, context-sensitive databases. Finally, beliefs can be changed by two distinct updating systems, with one hewing to more or less normatively appropriate methods of Bayesian updating, and the other relying on a psychological immune system, which functions to guard our most centrally held beliefs from potential inconsistency with newly formed beliefs. Understanding belief’s role in our cognitive economy allows us to illuminate broader real-world issues such as how fake news, propaganda, and brainwashing exploit our psychology of belief, and how best to construct our modern informational world.

In this chapter we summarize how economists conceptualize beliefs. Moving both backward and forward in time, we review the way that mainstream economics currently deals with beliefs, as well as, briefly, the history of economists’ thinking about beliefs. Most importantly, we introduce the reader to a recent, transformational movement in economics that focuses on belief-based utility. This approach challenges the standard economic assumption that beliefs are only an input to decision making and examines implications of the intuitive idea that people derive pleasure and pain directly from their beliefs. We also address the question of when and why people care about what other people believe. We close with a discussion of the implications of these insights for contemporary social issues such as political polarization and fake news.

The accelerating development of technological power over ourselves and our environment raises the stakes of getting our beliefs right. I suggest that we can significantly improve our processes of belief formation by increasing actively open-minded thinking (AOT). Actively open-minded thinking helps us form more accurate and well-rounded beliefs by increasing the depth and – more importantly – the breadth of information search and inference. Because individuals do not always have time for adequate investigation, AOT is also a valuable indicator of which epistemic authorities are most likely to have reached accurate conclusions via effective methods. It is associated with better reasoning across a wide variety of contexts, leading to beliefs that are more accurate, more complete, and less biased. Yet it is not regularly taught in schools, nor is it a feature of typical public discourse. I suggest several strategies for increasing this cognitive habit in school and society.

Belief is often formalized using tools of probability theory. However, probability theory often focuses on simple examples – like coin flips or basic parametric distributions – and these do not describe much about actual human thinking. I highlight some basic examples of the complexity and richness of human mental representations and review some work which attempts to marry plausible types of representations with probabilistic models of belief, one of the most exciting current directions in psychology and machine learning.

In this chapter, we consider a cultural evolutionary psychological framework for understanding the origin, maintenance and diffusion of beliefs, and illustrate the utility of such a framework with two case studies – religious belief systems and conspiracy theory beliefs. A cultural evolutionary psychology of belief considers four broad sets of interacting factors: the content of a belief, a belief’s fit with individual conditions, the social dynamics surrounding a belief, and the socioecological conditions that promote or suppress a belief. A cultural evolutionary psychology of belief overcomes the limitations to what we call standard evolutionary psychology, a school of thought that emphasizes the activation of innate cognitive modules for understanding the generation and spread of beliefs. With this chapter, then, we aim to show how social and cognitive science researchers can approach the study of beliefs from an evolutionary perspective without committing to the controversial assumptions of standard evolutionary psychology.

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.