Psychology is the science of the mind and behavior. The word "psychology" comes from the Greek word psyche meaning "breath, spirit, soul", and the Greek word logia meaning the study of something. According to Medilexicons medical dictionary, psychology is "The profession (clinical psychology), scholarly discipline (academic psychology), and science (research psychology) concerned with the behavior of humans and animals, and related mental and physiologic processes." Some Definitions-- Psychology is the scientific study of people, the mind and behavior. It is both a thriving academic discipline and a vital professional practice. (The British Psychological Society) The scientific study of the behavior of individuals and their mental processes. (American Psychological Association) Both these definitions tell us that psychology is fundamentally concerned with understanding behavior.

The word psychology derives from Greek roots meaning study of the psyche, or soul (ψυχή psukhē, "breath, spirit, soul" and -λογία -logia, "study of" or "research").The Latin word psychologia was first used by the Croatian humanist and Latinist Marko Marulić in his book, Psichiologia de ratione animae humanae in the late 15th century or early 16th century. The earliest known reference to the word psychology in English was by Steven Blankaart in 1694 in The Physical Dictionary which refers to "Anatomy, which treats the Body, and Psychology, which treats of the Soul." In 1890, William James defined psychology as "the science of mental life, both of its phenomena and their conditions". This definition enjoyed widespread currency for decades. However, this meaning was contested, notably by radical behaviorists such as John B. Watson, who in his 1913 manifesto defined the discipline of psychology as the acquisition of information useful to the control of behavior. Also since James defined it, the term more strongly connotes techniques of scientific experimentation. Folk psychology refers to the understanding of ordinary people, as contrasted with that of psychology professionals. In this field, a professional practitioner or researcher is called a psychologist and can be classified as a social, behavioral, or cognitive scientist. Psychologists explore behavior and mental processes, including perception, cognition, attention, emotion (affect), intelligence, phenomenology, motivation (conation), brain functioning, and personality. This extends to interaction between people, such as interpersonal relationships, including psychological resilience, family resilience, and other areas. Psychologists of diverse orientations also consider the unconscious mind.

The ancient civilizations of Egypt, Greece, China, India, and Persia all engaged in the philosophical study of psychology. Historians note that Greek philosophers, including Thales, Plato, and Aristotle (especially in his De Anima treatise),addressed the workings of the mind.As early as the 4th century BC, Greek physician Hippocrates theorized that mental disorders had physical rather than supernatural causes. In China, psychological understanding grew from the philosophical works of Laozi and Confucius, and later from the doctrines of Buddhism. Distinctions in types of awareness appear in the ancient thought of India, influenced by Hinduism. A central idea of the Upanishads is the distinction between a persons transient mundane self and their eternal unchanging soul. Divergent Hindu doctrines, and Buddhism, have challenged this hierarchy of selves, but have all emphasized the importance of reaching higher awareness. Yoga is a range of techniques used in pursuit of this goal. Much of the Sanskrit corpus was suppressed under the British East India Company followed by the British Raj in the 1800s. However, Indian doctrines influenced Western thinking via the Theosophical Society, a New Age group which became popular among Euro-American intellectuals. Psychology was a popular topic in Enlightenment Europe. In Germany, Gottfried Wilhelm Leibniz (1646–1716) applied his principles of calculus to the mind, arguing that mental activity took place on an indivisible continuum—most notably, that among an infinity of human perceptions and desires, the difference between conscious and unconscious awareness is only a matter of degree. Christian Wolff identified psychology as its own science, writing Psychologia empirica in 1732 and Psychologia rationalis in 1734. This notion advanced further under Immanuel Kant, who established the idea of anthropology, with psychology as an important subdivision. However, Kant explicitly and notoriously rejected the idea of experimental psychology, writing that "the empirical doctrine of the soul can also never approach chemistry even as a systematic art of analysis or experimental doctrine, for in it the manifold of inner observation can be separated only by mere division in thought, and cannot then be held separate and recombined at will (but still less does another thinking subject suffer himself to be experimented upon to suit our purpose), and even observation by itself already changes and displaces the state of the observed object." Having consulted philosophers Hegel and Herbart, in 1825 the Prussian state established psychology as a mandatory discipline in its rapidly expanding and highly influential educational system. However, this discipline did not yet embrace experimentation. In England, early psychology involved phrenology and the response to social problems including alcoholism, violence, and the countrys well-populated mental asylums.

Biological psychology, also known as physiological psychology, or neuropsychology is the study of the biological substrates of behavior and mental processes. Key research topics in this field include comparative psychology, which studies humans in relation to other animals, and perception which involves the physical mechanics of sensation as well as neural and mental processing. For centuries, a leading question in biological psychology has been whether and how mental functions might be localized in the brain. From Phineas Gage to H. M. and Clive Wearing, individual people with mental issues traceable to physical damage have inspired new discoveries in this area. Modern neuropsychology could be said to originate in the 1870s, when in France Paul Broca traced production of speech to the left frontal gyrus, thereby also demonstrating hemispheric lateralization of brain function. Soon after, Carl Wernicke identified a related area necessary for the understanding of speech. The contemporary field of behavioral neuroscience focuses on physical causes underpinning behavior. For example, physiological psychologists use animal models, typically rats, to study the neural, genetic, and cellular mechanisms that underlie specific behaviors such as learning and memory and fear responses. Cognitive neuroscientists investigate the neural correlates of psychological processes in humans using neural imaging tools, and neuropsychologists conduct psychological assessments to determine, for instance, specific aspects and extent of cognitive deficit caused by brain damage or disease. The biopsychosocial model is an integrated perspective toward understanding consciousness, behavior, and social interaction. It assumes that any given behavior or mental process affects and is affected by dynamically interrelated biological, psychological, and social factors. Evolutionary psychology examines cognition and personality traits from an evolutionary perspective. This perspective suggests that psychological adaptations evolved to solve recurrent problems in human ancestral environments. Evolutionary psychology offers complementary explanations for the mostly proximate or developmental explanations developed by other areas of psychology: that is, it focuses mostly on ultimate or "why?" questions, rather than proximate or "how?" questions. "How?" questions are more directly tackled by behavioral genetics research, which aims to understand how genes and environment impact behavior. The search for biological origins of psychological phenomena has long involved debates about the importance of race, and especially the relationship between race and intelligence. The idea of white supremacy and indeed the modern concept of race itself arose during the process of world conquest by Europeans. Carl von Linnaeuss four-fold classification of humans classifies Europeans as intelligent and severe, Americans as contented and free, Asians as ritualistic, and Africans as lazy and capricious. Race was also used to justify the construction of socially specific mental disorders such as drapetomania and dysaesthesia aethiopica—the behavior of uncooperative African slaves. After the creation of experimental psychology, "ethnical psychology" emerged as a subdiscipline, based on the assumption that studying primitive races would provide an important link between animal behavior and the psychology of more evolved humans.

Psychologists take human behavior as a main area of study. Much of the research in this area began with tests on mammals, based on the idea that humans exhibit similar fundamental tendencies. Behavioral research ever aspires to improve the effectiveness of techniques for behavior modification. Early behavioral researchers studied stimulus–response pairings, now known as classical conditioning. They demonstrated that behaviors could be linked through repeated association with stimuli eliciting pain or pleasure. Ivan Pavlov—known best for inducing dogs to salivate in the presence of a stimulus previous linked with food—became a leading figure in the Soviet Union and inspired followers to use his methods on humans.In the United States, Edward Lee Thorndike initiated "connectionism" studies by trapping animals in "puzzle boxes" and rewarding them for escaping. Thorndike wrote in 1911: "There can be no moral warrant for studying mans nature unless the study will enable us to control his acts." From 1910–1913 the American Psychological Association went through a sea change of opinion, away from mentalism and towards "behavioralism", and in 1913 John B. Watson coined the term behaviorism for this school of thought. Watsons famous Little Albert experiment in 1920 demonstrated that repeated use of upsetting loud noises could instill phobias (aversions to other stimuli) in an infant human.Karl Lashley, a close collaborator with Watson, examined biological manifestations of learning in the brain. Embraced and extended by Clark L. Hull, Edwin Guthrie, and others, behaviorism became a widely used research paradigm. A new method of "instrumental" or "operant" conditioning added the concepts of reinforcement and punishment to the model of behavior change. Radical behaviorists avoided discussing the inner workings of the mind, especially the unconscious mind, which they considered impossible to assess scientifically. Operant conditioning was first described by Miller and Kanorski and popularized in the U.S. by B. F. Skinner, who emerged as a leading intellectual of the behaviorist movement. Noam Chomsky delivered an influential critique of radical behaviorism on the grounds that it could not adequately explain the complex mental process of language acquisition.Martin Seligman and colleagues discovered that the conditioning of dogs led to outcomes ("learned helplessness") that opposed the predictions of behaviorism. Skinners behaviorism did not die, perhaps in part because it generated successful practical applications. Edward C. Tolman advanced a hybrid "cognitive behaviorial" model, most notably with his 1948 publication discussing the cognitive maps used by rats to guess at the location of food at the end of a modified maze. The Association for Behavior Analysis International was founded in 1974 and by 2003 had members from 42 countries. The field has been especially influential in Latin America, where it has a regional organization known as ALAMOC: La Asociación Latinoamericana de Análisis y Modificación del Comportamiento. Behaviorism also gained a strong foothold in Japan, where it gave rise to the Japanese Society of Animal Psychology (1933), the Japanese Association of Special Education (1963), the Japanese Society of Biofeedback Research (1973), the Japanese Association for Behavior Therapy (1976), the Japanese Association for Behavior Analysis (1979), and the Japanese Association for Behavioral Science Research (1994). Today the field of behaviorism is also commonly referred to as behavior modification or behavior analysis.

Cognitive psychology studies cognition, the mental processes underlying mental activity. Perception, attention, reasoning, thinking, problem solving, memory, learning, language, and emotion are areas of research. Classical 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 functionalism and experimental psychology. On a broader level, cognitive science is an interdisciplinary enterprise of cognitive psychologists, cognitive neuroscientists, researchers in artificial intelligence, linguists, human–computer interaction, computational neuroscience, logicians and social scientists. Computer simulations are sometimes used to model phenomena of interest. Baddeleys model of working memory Starting in the 1950s, the experimental techniques developed by Wundt, James, Ebbinghaus, and others re-emerged as experimental psychology became increasingly cognitivist—concerned with information and its processing—and, eventually, constituted a part of the wider cognitive science. Some called this development the cognitive revolution because it rejected the anti-mentalist dogma of behaviorism as well as the strictures of psychoanalysis. Social learning theorists, such as Albert Bandura, argued that the childs environment could make contributions of its own to the behaviors of an observant subject. The Müller–Lyer illusion. Psychologists make inferences about mental processes from shared phenomena such as optical illusions. Technological advances also renewed interest in mental states and representations. English neuroscientist Charles Sherrington and Canadian psychologist Donald O. Hebb used experimental methods to link psychological phenomena with the structure and function of the brain. The rise of computer science, cybernetics and artificial intelligence suggested the value of comparatively studying information processing in humans and machines. Research in cognition had proven practical since World War II, when it aided in the understanding of weapons operation. A popular and representative topic in this area is cognitive bias, or irrational thought. Psychologists (and economists) have classified and described a sizeable catalogue of biases which recur frequently in human thought. The availability heuristic, for example, is the tendency to overestimate the importance of something which happens to come readily to mind. Elements of behaviorism and cognitive psychology were synthesized to form cognitive behavioral therapy, a form of psychotherapy modified from techniques developed by American psychologist Albert Ellis and American psychiatrist Aaron T. Beck. Cognitive psychology was subsumed along with other disciplines, such as philosophy of mind, computer science, and neuroscience, under the cover discipline of cognitive science.

Social psychology studies the nature and causes of social behavior. Social psychology is the study of how humans think about each other and how they relate to each other. Social psychologists study such topics as the influence of others on an individuals behavior (e.g. conformity, persuasion), and the formation of beliefs, attitudes, and stereotypes about other people. Social cognition fuses elements of social and cognitive psychology in order to understand how people process, remember, or distort social information. The study of group dynamics reveals information about the nature and potential optimization of leadership, communication, and other phenomena that emerge at least at the microsocial level. 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. The study of human society is therefore a potentially valuable source of information about the causes of psychiatric disorder. Some sociological concepts applied to psychiatric disorders are the social role, sick role, social class, life event, culture, migration, social, and total institution.

Psychoanalysis comprises a method of investigating the mind and interpreting experience; a systematized set of theories about human behavior; and a form of psychotherapy to treat psychological or emotional distress, especially conflict originating in the unconscious mind. This school of thought originated in the 1890s with Austrian medical doctors including Josef Breuer (physician), Alfred Adler (physician), Otto Rank (psychoanalyst), and most prominently Sigmund Freud (neurologist). Freuds psychoanalytic theory was largely based on interpretive methods, introspection and clinical observations. It became very well known, largely because it tackled subjects such as sexuality, repression, and the unconscious. These subjects were largely taboo at the time, and Freud provided a catalyst for their open discussion in polite society. Clinically, Freud helped to pioneer the method of free association and a therapeutic interest in dream interpretation. Swiss psychiatrist Carl Jung, influenced by Freud, elaborated a theory of the collective unconscious—a primordial force present in all humans, featuring archetypes which exerted a profound influence on the mind. Jungs competing vision formed the basis for analytical psychology, which later led to the archetypal and process-oriented schools. Other well-known psychoanalytic scholars of the mid-20th century include Erik Erikson, Melanie Klein, D. W. Winnicott, Karen Horney, Erich Fromm, John Bowlby, and Sigmund Freuds daughter, Anna Freud. Throughout the 20th century, psychoanalysis evolved into diverse schools of thought which could be called Neo-Freudian. Among these schools are ego psychology, object relations, and interpersonal, Lacanian, and relational psychoanalysis. Psychologists such as Hans Eysenck and philosophers including Karl Popper criticized psychoanalysis. Popper argued that psychoanalysis had been misrepresented as a scientific discipline, whereas Eysenck said that psychoanalytic tenets had been contradicted by experimental data. By the end of 20th century, psychology departments in American universities mostly marginalized Freudian theory, dismissing it as a "desiccated and dead" historical artifact. However, researchers in the emerging field of neuro-psychoanalysis today defend some of Freuds ideas on scientific grounds, while scholars of the humanities maintain that Freud was not a "scientist at all, but ... an interpreter".

Humanistic psychology developed in the 1950s as a movement within academic psychology, in reaction to both behaviorism and psychoanalysis. The humanistic approach sought to glimpse the whole person, not just fragmented parts of the personality or isolated cognitions. Humanism focused on uniquely human issues, such as free will, personal growth, self-actualization, self-identity, death, aloneness, freedom, and meaning. It emphasized subjective meaning, rejection of determinism, and concern for positive growth rather than pathology.[citation needed] Some founders of the humanistic school of thought were American psychologists Abraham Maslow, who formulated a hierarchy of human needs, and Carl Rogers, who created and developed client-centered therapy. Later, positive psychology opened up humanistic themes to scientific modes of exploration. The American Association for Humanistic Psychology, formed in 1963, declared: Humanistic psychology is primarily an orientation toward the whole of psychology rather than a distinct area or school. It stands for respect for the worth of persons, respect for differences of approach, open-mindedness as to acceptable methods, and interest in exploration of new aspects of human behavior. As a "third force" in contemporary psychology, it is concerned with topics having little place in existing theories and systems: e.g., love, creativity, self, growth, organism, basic need-gratification, self-actualization, higher values, being, becoming, spontaneity, play, humor, affection, naturalness, warmth, ego-transcendence, objectivity, autonomy, responsibility, meaning, fair-play, transcendental experience, peak experience, courage, and related concepts. In the 1950s and 1960s, influenced by philosophers Søren Kierkegaard and Martin Heidegger and, psychoanalytically trained American psychologist Rollo May pioneered an existential branch of psychology, which included existential psychotherapy: a method based on the belief that inner conflict within a person is due to that individuals confrontation with the givens of existence. Swiss psychoanalyst Ludwig Binswanger and American psychologist George Kelly may also be said to belong to the existential school. Existential psychologists differed from more "humanistic" psychologists in their relatively neutral view of human nature and their relatively positive assessment of anxiety. Existential psychologists emphasized the humanistic themes of death, free will, and meaning, suggesting that meaning can be shaped by myths, or narrative patterns, and that it can be encouraged by an acceptance of the free will requisite to an authentic, albeit often anxious, regard for death and other future prospects. Austrian existential psychiatrist and Holocaust survivor Viktor Frankl drew evidence of meanings therapeutic power from reflections garnered from his own internment. He created a variation of existential psychotherapy called logotherapy, a type of existentialist analysis that focuses on a will to meaning (in ones life), as opposed to Adlers Nietzschean doctrine of will to power or Freuds will to pleasure.

Personality is concerned with enduring patterns of behavior, thought, and emotion—commonly referred to as personality—in individuals. 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 id, ego, and super-ego. In order to develop a taxonomy of personality constructs, trait theorists, in contrast, attempt to describe the personality sphere in terms of a discrete number of key traits using the statistical data-reduction method of factor analysis. Although the number of proposed traits has varied widely, an early biologically-based model proposed by Hans Eysenck, the 3rd mostly highly cited psychologist of the 20th Century (after Freud, and Piaget respectively), suggested that at least three major trait constructs are necessary to describe human personality structure: extraversion–introversion, neuroticism-stability, and psychoticism-normality. Raymond Cattell, the 7th most highly cited psychologist of the 20th Century (based on the scientific peer-reviewed journal literature) empirically derived a theory of 16 personality factors at the primary-factor level, and up to 8 broader second-stratum factors (at the Eysenckian level of analysis), rather than the "Big Five" dimensions. Dimensional models of personality are receiving increasing support, and a version of dimensional assessment has been included in the DSM-V. However, despite a plethora of research into the various versions of the "Big Five" personality dimensions, it appears necessary to move on from static conceptualizations of personality structure to a more dynamic orientation, whereby it is acknowledged that personality constructs are subject to learning and change across the lifespan. An early example of personality assessment was the Woodworth Personal Data Sheet, constructed during World War I. The popular, although psychometrically inadequate sought to assess individuals "personality types" according to the personality theories of Carl Jung. Behaviorist resistance to introspection led to the development of the Strong Vocational Interest Blank and Minnesota Multiphasic Personality Inventory (MMPI), in an attempt to ask empirical questions that focused less on the psychodynamics of the respondent. However, the MMPI has been subjected to critical scrutiny, given that it adhered to archaic psychiatric nosology, and since it required individuals to provide subjective, introspective responses to the hundreds of items pertaining to psychopathology.