Philosophical and scientific roots 
The study of psychology in
philosophical context dates back to the ancient civilizations of
Egypt,
Greece, China, and
India. Psychology began adopting a more
clinical[1] and
experimental[2] approach under medieval
Muslim psychologists and
physicians, who built
psychiatric hospitals for such purposes.
[3]Though the use of psychological
experimentation dates back to
Alhazen's Book of Optics in 1021,
[2][4] psychology as an independent experimental field of study began in 1879, when
Wilhelm Wundt founded the first laboratory dedicated exclusively to psychological research at
Leipzig University in Germany, for which Wundt is known as the "father of psychology".
[5] The year 1879 is thus sometimes regarded as the "birthdate" of psychology. The American philosopher
William James published his seminal book,
Principles of Psychology,
[6] in 1890, while laying the foundations for many of the questions that
psychologists would focus on for years to come. Other important early contributors to the field include
Hermann Ebbinghaus (1850–1909), a pioneer in the experimental study of
memory at the
University of Berlin; and the Russian
physiologist Ivan Pavlov (1849-1936), who investigated the
learning process now referred to as
classical conditioning. [
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PsychoanalysisMainarticle:
PsychoanalysisFrom the 1890s until his death in 1939, the
Austrian physician
Sigmund Freud developed a method of
psychotherapy known as
psychoanalysis. Freud was a neurologist whose understanding of the mind was largely based on interpretive methods,
introspection and clinical observations, and was focused in particular on resolving unconscious conflict, mental distress and
psychopathology. Freud's theories became very well-known, largely because they tackled subjects such as
sexuality,
repression, and the
unconscious mind as general aspects of psychological development. These were largely considered
taboo subjects at the time, and Freud provided a catalyst for them to be openly discussed in polite society. While Freud is perhaps best known for his tripartite model of the mind, consisting of the
id,
ego, and
superego, and his theories about the
Oedipus complex, his most lasting legacy may be not the content of his theories but his clinical innovations, such as the method of
free association and a clinical interest in dreams. Freud also had a significant influence on
Carl Jung, whose
analytical psychology became an alternative form of
depth psychology. Other well-known psychoanalytic thinkers of the mid-twentieth century included
Erik Erickson,
Anna Freud,
Melanie Klein,
D.W. Winnicott,
Karen Horney,
Erich Fromm, and
John Bowlby.
Philosopher Karl Popper argued that Freud's psychoanalytic theories were presented in
untestable form.
[7] Psychology departments in American universities today are scientifically oriented, and Freudian theory has been marginalized, being regarded instead as a "desiccated and dead" historical artifact, according to a recent
APA study.
[8]Contemporary psychoanalysis comprises diverse schools of thought, including ego psychology, object relations, interpersonal, Lacanian, and relational psychoanalysis. Modification of Jung's theories has led to the
archetypal and
process-oriented schools of psychological thought. [
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BehaviorismMain article:
BehaviorismFounded by
John B. Watson and embraced and extended by
Edward Thorndike,
Clark L. Hull,
Edward C. Tolman, and later
B.F. Skinner. Founders of early psychology in the late 19th and early part of the 20th century, Wilhelm Wundt and William James, studied the mind via
introspection. During the early decades of the 20th century
behaviorism gained popularity as a guiding psychological theory. The behaviorists (e.g. Watson) argued the contents of the mind were not open to scientific scrutiny and that scientific psychology should only be concerned with the study of observable behavior. There was no consideration of the internal representation or the mind. The rise of behaviorism was partly due to the success of laboratory based animal experimentation and partly in reaction to Freudian
psychodynamics which tended to rely on case studies and clinical experience. Freud's theories and practice focused on the resolution unconscious conflict often arising from childhood experiences to treat psychological trauma and psychosis. However, it was argued that Freud's theories were difficult to test empirically.Behaviorism differs from other perspectives in a number of ways. Behaviorists focus on behavior-environment relations and analyze overt and covert (i.e., private) behavior as a function of the organism interacting with its environment
[9]. Behaviorists do not reject the study of covert or private events (e.g., dreaming). What behaviorists reject is an autonomous causal entity inside the organism that causes overt (e.g., walking, talking) or covert (e.g., dreaming, imagining) behavior. Concepts such as "mind" or "consciousness" are not used by behaviorists because such terms do not describe actual psychological events (such as imagining) but are used as explanatory entities hidden somewhere in the organism. By contrast, behaviorism treats private events as behavior, and analyzes them in the same way as overt behavior (hence the name "behaviorism"). Behavior refers to the concrete events of the organism, overt or private.Linguist
Noam Chomsky's critique of the behaviorist model of language acquisition is regarded by many as a key turning point in the decline in the prominence of the theory of behaviorism generally.
[10] But Skinner's behaviorism has not died, perhaps in part because it has generated successful practical applications.
[10] The ascendancy of behaviorism as an overarching model in psychology, however, gave way to the next dominant paradigm, cognitive approaches.
[11] [
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Humanism and existentialismMain article:
Humanistic psychologyHumanistic psychology was developed in the 1950s in reaction to both behaviorism and psychoanalysis. By using
phenomenology,
intersubjectivity and first-person categories, the humanistic approach seeks to glimpse the whole person--not just the fragmented parts of the personality or cognitive functioning.
[12] Humanism focuses on uniquely human issues and fundamental issues of life, such as self-identity, death, aloneness, freedom, and meaning. There are several factors which distinguish the Humanistic Approach from other approaches within psychology, including the emphasis on subjective meaning, a rejection of determinism, and a concern for positive growth rather than pathology. Some of the founding theorists behind this school of thought were
Abraham Maslow who formulated a
hierarchy of human needs,
Carl Rogers who created and developed
Client-centered therapy, and
Fritz Perls who helped create and develop
Gestalt therapy. It became so influential as to be called the "third force" within psychology (along with behaviorism and psychoanalysis).
[13]Influenced largely by the work of German philosopher
Martin Heidegger and Danish philosopher
Søren Kierkegaard, psychoanalytically-trained
Rollo May developed an
existential breed of psychology in the 1950s and 1960s. Existential psychologists argued that people must come to terms with their mortality and that, in so doing, people will be obligated to accept that they are free—that they possess
free will and are at liberty to defy expectations and conventions in order to forge their own, meaningful paths through life. May believed that an important element of the meaning-making process is the search for
myths, or narrative patterns into which the individual may fit.
[14]From the existential perspective, not only does the quest for meaning follow from an acceptance of mortality, but the attainment of meaning can overshadow the prospect of death. As existential psychiatrist and
Holocaust survivor
Viktor Frankl observed,
[15]We who lived in concentration camps can remember the men who walked through the huts comforting others, giving away their last piece of bread. They may have been few in number, but they offer sufficient proof that everything can be taken from a man but one thing: the last of the human freedoms—to choose one's attitude in any given set of circumstances, to choose one's own way.
[16]In addition to May and Frankl, psychoanalyst
Ludwig Binswanger and psychologist
George Kelly may be said to belong to the existential school.
[17]Both existential and humanistic psychologists argue that people should strive to reach their full potential, but only humanistic psychologists believe that this striving is innate. For existential psychologists, the striving only follows an anxiety-producing contemplation of mortality, freedom, and responsibility.
[18] [
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CognitivismMain article:
Cognitive psychologyBehaviorism was the dominant paradigm in American psychology throughout the first half of the 20th century. However, the modern field of psychology largely came to be dominated by
cognitive psychology. Linguist
Noam Chomsky's 1959 review of B. F. Skinner's Verbal Behavior challenged the behaviorist approaches to studies of behavior and language dominant at the time and contributed to the
cognitive revolution in psychology. Chomsky was highly critical of what he considered arbitrary notions of 'stimulus', 'response' and 'reinforcement' which Skinner borrowed from animal experiments in the laboratory. Chomsky argued that Skinner's notions could only be applied to complex human behavior, such as
language acquisition, in a vague and superficial manner. Chomsky emphasized that research and analysis must not ignore the contribution of the child in the acquisition of language and proposed that humans are born with a natural ability to
acquire language.
[19] Work most associated with psychologist
Albert Bandura, who initiated and studied
social learning theory, showed that children could learn aggression from a role model through
observational learning, without any change in overt behavior, and so must be accounted for by internal processes.
[20]With the rise of computer science and
artificial intelligence, analogies were drawn between
information processing by humans and information processing by machines. This, combined with the assumptions that (1) mental representations exist and, (2) mental states and operations could be inferred through scientific experimentation in the laboratory, led to the rise of
cognitivism as a popular model of the mind. Research in cognition was also backed by the aim to gain a better understanding weapons operation since World war II.
[21] Cognitive psychology differs from other psychological perspectives in two key ways. First, it accepts the use of the scientific method, and generally rejects introspection as a method of investigation, unlike symbol-driven approaches such as Freudian psychodynamics. Second, it explicitly acknowledges the existence of internal mental states (such as belief, desire and motivation), whereas behaviorism does not.Preceding the cognitive revolution, German psychologist
Hermann Ebbinghaus (1880s) pioneered the experimental study of memory, arguing that higher mental processes are not hidden from view, but instead could be studied using experimentation.
[22] Links between
brain and
nervous system function also became understood, partly due to the experimental work of people such as
Charles Sherrington and
Donald Hebb, and partly due to studies of people with
brain injury (see
cognitive neuropsychology). With the development of technologies for measuring brain function,
neuropsychology and
cognitive neuroscience have become increasingly active areas of contemporary psychology. Cognitive psychology has been subsumed along with other disciplines, such as
philosophy of mind,
computer science, and
neuroscience, under the umbrella discipline of
cognitive science.[
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Schools of thoughtMain article:
List of psychological schoolsVarious schools of thought have argued for a particular model to be used as a guiding theory by which all, or the majority, of human behavior can be explained. The popularity of these has waxed and waned over time. Some
psychologists may think of themselves as adherents to a particular school of thought and reject the others, although most consider each as an approach to understanding the mind, and not necessarily as mutually exclusive theories. On the basis of
Tinbergen's four questions a framework of reference of all fields of psychological research can be established (including anthropological research and humanities).In modern times, psychology has adopted an integrated perspective towards understanding consciousness, behavior, and social interaction. This perspective is commonly referred to as the
biopsychosocial approach. The basic tenet of the biopsychosocial model is that any given behavior or mental process affect and are affected by dynamically interrelated biological, psychological, and social factors.
[23] The psychological aspect refers to the role that cognition and emotions play in any given psychological phenomenon. For example, the effect of mood or beliefs and expectations on an individual's reactions to an event. The biological aspect refers to the role of biological factors in psychological phenomena. For example, the effect of the prenatal environment on brain development and cognitive abilities, or the influence of genes on individual dispositions. The socio-cultural aspect refers to the role that social and cultural environments play in a given psychological phenomenon. For example, the role of parental or peer influence in the behaviors or characteristics of an individual.Subfields Psychology encompasses a vast domain, and includes many different approaches to the study of mental processes and behavior. Below are the major areas of inquiry that comprise psychology. A comprehensive list of the sub-fields and areas within psychology can be found at the
list of psychology topics and
list of psychology disciplines. [
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Abnormal psychologyMain article:
Abnormal psychologyAbnormal psychology is the study of
abnormal behavior in order to describe, predict, explain, and change abnormal patterns of functioning. Abnormal psychology studies the nature of
psychopathology and its causes, and this knowledge is applied in
clinical psychology to treat a patient with psychological disorders.In the study of abnormal behavior, it can be difficult to define the line between which behaviors are considered normal and which are not. In general, abnormal behaviors must be maladaptive and cause an individual subjective discomfort (signs of emotional distress). According to the DSM-IV-TR, behaviors may be considered abnormal if they are associated with disability, personal distress, the violation of social norms, or dysfunction.
[24] [
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Biological psychology
Main articles:
Biological psychology,
Neuropsychology,
Physiological psychology,
Cognitive neuroscience, and
Evolutionary psychologyMRI depicting the human brain. The arrow indicates the position of the
hypothalamus.Biological psychology is the scientific study of the biological bases of behavior and mental states. Seeing all behavior as controlled by the nervous system, biological psychologists feel it is sensible to study how the
brain functions in order to understand behavior. This is the approach taken in
behavioral neuroscience,
cognitive neuroscience, and
neuropsychology. Neuropsychology is the branch of psychology that aims to understand how the structure and function of the 'brain' relate to specific behavioral and psychological processes. Neuropsychology is particularly concerned with the understanding of brain injury in an attempt to work out normal psychological function. The approach of cognitive neuroscience to studying the link between brain and behavior is to use neuroimaging tools, such as to observe which areas of the brain are active during a pa [
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Cognitive psychologyMain article:
Cognitive psychologyCognitive psychology studies
cognition, the
mental processes underlying behavior. It uses
information processing as a framework for understanding the mind.
Perception,
learning,
problem solving,
memory,
attention,
language and
emotion are all well researched areas. Cognitive psychology is associated with a school of thought known as
cognitivism, whose adherents argue for an
information processing model of mental function, informed by
positivism and
experimental psychology.On a broader level,
Cognitive science is a conjoined enterprise of cognitive psychologists,
neurobiologists, workers in
artificial intelligence,
logicians,
linguists, and social scientists, and places a slightly greater emphasis on computational theory and formalization. Both areas can use
computational models to simulate phenomena of interest. Because mental events cannot directly be observed, computational models provide a tool for studying the functional organization of the mind. Such models give cognitive psychologists a way to study the "software" of mental processes independent of the "hardware" it runs on, be it the brain or a computer. [
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Comparative psychologyMain article:
Comparative psychologyComparative psychology refers to the study of the behavior and mental life of
animals other than human beings. It is related to disciplines outside of psychology that study animal behavior, such as
ethology. Although the field of psychology is primarily concerned with humans, the behavior and mental processes of
animals is also an important part of psychological research, either as a subject in its own right (e.g.,
animal cognition and ethology), or with strong emphasis about evolutionary links, and somewhat more controversially, as a way of gaining an insight into human psychology by means of comparison or via animal models of emotional and behavior systems as seen in neuroscience of psychology (e.g.,
affective neuroscience and
social neuroscience).[
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Counseling psychologyMain article:
Counseling psychologyCounseling psychology seeks to facilitate personal and
interpersonal functioning across the lifespan with a focus on emotional, social,
vocational, educational, health-related, developmental, and organizational concerns. Counselors are primarily clinicians, using psychotherapy and other interventions in order to treat clients. Traditionally, counseling psychology has focused more on normal developmental issues and everyday
stress rather than psychopathology, but this distinction has softened over time. Counseling psychologists are employed in a variety of settings, including universities, hospitals, schools, governmental organizations, businesses, private practice, and community mental health centers. [
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Clinical psychologyMain article:
Clinical psychologyClinical psychology includes the study and application of psychology for the purpose of understanding, preventing, and relieving psychologically-based distress or
dysfunction and to promote subjective
well-being and personal development. Central to its practice are psychological assessment and
psychotherapy, although clinical psychologists may also engage in research, teaching, consultation, forensic testimony, and program development and administration.
[25] Some clinical psychologists may focus on the clinical management of patients with
brain injury—this area is known as
clinical neuropsychology. In many countries clinical psychology is a regulated
mental health profession.The work performed by clinical psychologists tends to be done inside various therapy models, all of which involve a formal relationship between professional and client—usually an individual, couple, family, or small group—that employs a set of procedures intended to form a therapeutic alliance, explore the nature of psychological problems, and encourage new ways of thinking, feeling, or behaving. The four major perspectives are
Psychodynamic,
Cognitive Behavioral,
Existential-Humanistic, and
Systems or Family therapy. There has been a growing movement to integrate these various therapeutic approaches, especially with an increased understanding of issues regarding culture, gender, spirituality, and sexual-orientation. With the advent of more robust research findings regarding psychotherapy, there is growing evidence that most of the major therapies are about of equal effectiveness, with the key common element being a strong therapeutic alliance.
[26][27] Because of this, more training programs and psychologists are now adopting an
eclectic therapeutic orientation. [
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Developmental psychologyMain article:
Developmental psychologyMainly focusing on the development of the human mind through the life span,
developmental psychology seeks to understand how people come to perceive, understand, and act within the world and how these processes change as they age. This may focus on intellectual, cognitive, neural, social, or
moral development. Researchers who study children use a number of unique research methods to make observations in natural settings or to engage them in experimental tasks. Such tasks often resemble specially designed games and activities that are both enjoyable for the child and scientifically useful, and researchers have even devised clever methods to study the mental processes of small infants. In addition to studying children, developmental psychologists also study
aging and processes throughout the life span, especially at other times of rapid change (such as adolescence and old age). Developmental psychologists draw on the full range of theorists in scientific psychology to inform their research. [
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Educational psychologyMain article:
Educational psychologyEducational psychology is the study of how humans learn in
educational settings, the effectiveness of educational interventions, the psychology of teaching, and the
social psychology of
schools as organizations. The work of child psychologists such as
Lev Vygotsky,
Jean Piaget and
Jerome Bruner has been influential in creating
teaching methods and educational practices.[
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Forensic psychologyMain article:
Forensic psychologyForensic psychology covers a broad range of practices primarily involving clinical
evaluations of
defendants, reports to judges and attorneys, and courtroom testimony on given issues. Forensic psychologists are appointed by the court to conduct competency to stand trial evaluations, competency to be executed evaluations, sanity evaluations, involuntary commitment evaluations, provide sentencing recommendations, and sex offender evaluation and treatment evaluations and provide recommendations to the court through written reports and testimony. Most of the questions the court asks the forensic psychologist are not questions of psychology but rather legal questions. For example, there is no definition of sanity in psychology. Rather, sanity is a legal definition that varies from place to place throughout the world. Therefore, a prime qualification of a forensic psychologist is an intimate understanding of the law, especially criminal law. [
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Health psychologyMain article:
Health psychologyHealth psychology is the application of psychological theory and research to health, illness and health care. Whereas clinical psychology focuses on mental health and neurological illness,
health psychology is concerned with the psychology of a much wider range of health-related behavior including healthy eating, the doctor-patient relationship, a patient's understanding of health information, and beliefs about illness. Health psychologists may be involved in public health campaigns, examining the impact of illness or health policy on
quality of life and in research into the psychological impact of health and social care. [
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Industrial/organizational psychologyMain article:
Industrial and organizational psychologyIndustrial and organizational psychology (I/O) applies psychological concepts and methods to optimize human potential in the workplace. Personnel psychology, a subfield of I/O psychology, applies the methods and principles of psychology in selecting and evaluating workers. I/O psychology's other subfield,
organizational psychology, examines the effects of work environments and management styles on worker motivation, job satisfaction, and productivity.
[28] [
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Personality psychologyMain article:
Personality psychologyPersonality psychology studies enduring patterns of
behavior,
thought, and
emotion in individuals, commonly referred to as
personality. Theories of personality vary across different psychological schools and orientations. They carry different assumptions about such issues as the role of the
unconscious and the importance of childhood experience. According to Freud, personality is based on the dynamic interactions of the ego, superego, and id.
[29] Trait theorists, in contrast, attempt to analyze personality in terms of a discrete number of key traits by the statistical method of
factor analysis. The number of proposed traits has varied widely. An early model proposed by
Hans Eysenck suggested that there are three traits that comprise human personality:
extraversion-introversion,
neuroticism, and
psychoticism.
Raymond Cattell proposed a theory of
16 personality factors. The "
Big Five" or Five Factor Model, proposed by
Lewis Goldberg currently has strong support among trait theorists. [
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Psychology and LawMain article:
Legal psychologyPsychology and law (or
Legal psychology) is a research-oriented field populated with researchers from several different areas within psychology (although
social and
cognitive psychologists are typical). Legal psychologists explore such topics as jury decision-making, eyewitness memory, scientific evidence, and legal policy. The term "legal psychology" has only recently come into use, and typically refers to any non-clinical law-related research. [
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Quantitative psychologyMain article:
Quantitative psychologyQuantitative psychology involves the application of
mathematical and
statistical modeling in psychological research, and the development of statistical methods for analyzing and explaining behavioral data. The term Quantitative psychology is relatively new and little used (only recently have Ph.D. programs in quantitative psychology been formed), and it loosely covers the longer standing subfields
psychometrics and
mathematical psychology.
Psychometrics is the field of psychology concerned with the theory and technique of psychological
measurement, which includes the measurement of
knowledge,
abilities,
attitudes, and
personality traits. Measurement of these unobservable
phenomena is difficult, and much of the research and accumulated knowledge in this discipline has been developed in an attempt to properly define and quantify such phenomena. Psychometric research typically involves two major research tasks, namely: (i) the construction of
instruments and procedures for measurement; and (ii) the development and refinement of theoretical approaches to measurement.Whereas
psychometrics is mainly concerned with
individual differences and
population structure,
mathematical psychology is concerned with modeling of
mental and
motor processes of the average individual.
Psychometrics is more associated with educational psychology,
personality, and clinical psychology.
Mathematical psychology is more closely related to
psychonomics/
experimental and
cognitive, and
physiological psychology and (
cognitive)
neuroscience. [
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Social psychologyMain article:
Social psychology (psychology)Social psychology studies the nature and causes of social behavior.
Social psychology is the study of social behavior and mental processes, with an emphasis on how humans think about each other and how they relate to each other. Social psychologists are especially interested in how people react to social situations. They study such topics as the influence of others on an individual's behavior (e.g.
conformity,
persuasion), and the formation of beliefs,
attitudes, and
stereotypes about other people.
Social cognition is a popular approach and involves cognitive and experimental methods for understanding social behavior. The study of
group dynamics is another important area of study in social psychology. In recent years, many social psychologists have become increasingly interested in
implicit measures,
mediational models, and the interaction of both person and social variables in accounting for behavior. [
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School psychologyMain article:
School psychologySchool psychology combines principles from
educational psychology and
clinical psychology to understand and treat students with learning disabilities; to foster the intellectual growth of "gifted" students; to facilitate pro social behaviors in adolescents; and otherwise to promote safe, supportive, and effective learning environments. School psychologists are trained in educational and behavioral assessment, intervention, prevention, and consultation, and many have extensive training in research.
[30] Currently, school psychology is the only field in which a professional can be called a "psychologist" without a doctoral degree, with the
National Association of School Psychologists (NASP) recognizing the
Specialist degree as the entry level. This is a matter of controversy as the
APA does not recognize anything below a doctorate as the entry level for a psychologist. Specialist-level school psychologists, who typically receive three years of graduate training, function almost exclusively within school systems, while those at the doctoral-level are found in a number of other settings as well, including universities, hospitals, clinics, and private practice
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