As a result, modern psychology is an amalgam of stances, theories and perspective that supplement or contradict each other.
Functional psychology or functionalism is a broad psychological school that became popular in the early decades of 20th century. Advocates of functional approach focused on the active (functional) adaptation of human consciousness to the environment (Vandenbos, 2006). Functional psychology relied on the work of William James, a pioneering American psychologist and philosopher, and the evolutionary theory developed of Charles Darwin. The primary concern of functionalists was to understand how the human mind and consciousness functions. Functionalists believed that this could be done via introspection: "Functionalists studied the mind not from the standpoint of its composition-its mental elements of structure-but rather as a conglomerate or accumulation of functions and processes that lead to practical consequences in the real world" (Schultz, & Schultz, 2008, p.145). As a result, functionalists rejected the traditional positivist philosophy of experimental research and advocated the potential of rational thought being concerned with the capability of the mind and practical value of psychological research.
The essence of functional psychology was articulated by John Dewey, the brightest representative of functionalism, in his "The Reflex Arc Concept in Psychology" (1896). Dewey criticized the notion of elementarism and atomism that dominated early psychology. His criticism also covered the emerging school of behaviorism with its stimulus-response theory (Dewey, 1964). Although functional psychology failed to become a formal school, the concepts and principles formulated by representatives of this approach contributed greatly to the development of behavioral psychology (Schultz, & Schultz, 2008). An essential contribution of functionalism was recognition of the validity of research involving animals, children and people with psychiatric disabilities. Yet the most important contribution of functionalism to contemporary psychological practice was introduction of novel research methods and techniques such as mental tests, questionnaires and physiological measures (Biro, & Shahan, 1982). This legacy continues to play critically important role in modern psychological practice.
The origins of behaviorist perspective, a theory successfully applied in modern psychological practice can be traced back to John Watson (1878 - 1958) whom was the first theorist to formulate the principles of modern behaviorism. His definition of this approach was highly practical: Watson believed psychology should be a purely objective field of knowledge used to accurately predict and control human behavior. Introspection and self-analysis in psychology were announced useless; besides Watson stated there were no difference between humans and animals thus neglecting the concept of the conscious and unconscious as such (Watson, 1913).
Watson relied primarily on the Ivan Pavlov's discovery of the mechanism of classical conditioning. Pavlov's studies of dog's digestion transformed the common understanding of learning and behavior. The scientist carried out a series of experiments