Timeline of Psychology
Psychology as a science and profession, from Aristotle's treatise on the soul in the 4th century BCE through Wundt's Leipzig laboratory, behaviorism, the cognitive revolution and the DSM to the replication crisis of 2011 – 2026.
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- 34 events 4th century BCE – 2026
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4th century BCE: Aristotle writes a treatise on the soul
In "On the Soul" ("De Anima"), probably written in his later years in Athens, Aristotle defined the soul (psyche) as the form of a living body and ranked its capacities: nutrition in plants, perception and movement in animals, and thought in humans. Unlike Alcmaeon of Croton, who had placed the mind in the brain, he made the heart the seat of sensation.
https://en.wikipedia.org/wiki/On_the_Soul1020s: Avicenna maps the faculties of the soul
In the section on the soul of his "Book of Healing" ("Kitab al-Shifa"), the Persian philosopher Avicenna (Ibn Sina) placed internal senses such as imagination, estimation and memory in the front, middle and rear ventricles of the brain, and argued with his "floating man" thought experiment that a person cut off from all sensation would still know that they exist. Translated into Latin in 12th-century Toledo, his scheme of faculties long remained standard in European philosophy handbooks.
https://en.wikipedia.org/wiki/The_Book_of_Healing1649: Descartes publishes "The Passions of the Soul"
In his last book, dedicated to Princess Elisabeth of Bohemia, René Descartes explained emotions as effects on an immaterial thinking soul of "animal spirits" moving through the nerves, and held that soul and body interact at the pineal gland. His sharp division, set out in earlier works, between a thinking mind and a body that works like a machine became the classic form of mind–body dualism.
https://en.wikipedia.org/wiki/Passions_of_the_Soul1689: Locke argues the mind is furnished by experience
In "An Essay Concerning Human Understanding", whose title page bears the date 1690, John Locke rejected innate ideas and likened the mind before experience to "white paper" filled by sensation and reflection. His phrase "association of ideas", from a chapter added in 1700, named the associationism that David Hartley developed in 1749 into a general theory of mind tied to the nerves.
https://en.wikipedia.org/wiki/An_Essay_Concerning_Human_Understanding1860: Fechner founds psychophysics
In "Elements of Psychophysics", Gustav Fechner, a former Leipzig physics professor, set out experimental methods for measuring sensation and proposed that perceived intensity grows with the logarithm of stimulus intensity, generalizing Ernst Heinrich Weber's finding of 1834 that the smallest noticeable difference between two weights is a constant fraction of the weight. His threshold methods are still used; his law fails for very weak and very strong stimuli.
https://en.wikipedia.org/wiki/Psychophysics1861: Broca locates a speech area in the frontal lobe
Paul Broca performed an autopsy on Louis Victor Leborgne, a Paris hospital patient who for years could say little but "tan" yet understood speech, and found damage in the left frontal lobe; by 1865 further cases led him to tie speech production to the left hemisphere. The cases provided influential anatomical evidence that specific mental functions depend on particular regions of the cortex, an idea earlier promoted on weak grounds by phrenology.
https://en.wikipedia.org/wiki/Broca%27s_area1872: Darwin traces emotional expressions to animal ancestry
In "The Expression of the Emotions in Man and Animals", Charles Darwin argued that expressions such as smiling, frowning and baring the teeth are inherited, largely shared across human cultures and paralleled in other animals, drawing on a questionnaire sent to observers abroad, photographs and tests in which friends and family judged emotions from faces. Paul Ekman's cross-cultural studies of facial expression revived the approach from the late 1960s.
https://en.wikipedia.org/wiki/The_Expression_of_the_Emotions_in_Man_and_Animals1879: Wundt opens a psychology laboratory in Leipzig
Wilhelm Wundt, a Leipzig philosophy professor and former assistant to Hermann von Helmholtz, began independent experiments in rooms the university had given him in 1876; it recognized the laboratory officially in 1883. Widely regarded as the first laboratory devoted to experimental psychology, though William James had taught experimental psychology at Harvard from 1875, it trained students from many countries.
https://en.wikipedia.org/wiki/Wilhelm_Wundt1884: Galton opens an anthropometric laboratory in London
At the International Health Exhibition in London, Francis Galton's laboratory charged visitors a small fee to measure traits such as height, weight and eyesight, collecting data on more than 9,000 people, from which he went on to develop correlation in 1888. Galton, who coined "eugenics" in 1883 and promoted it, pioneered the statistical study of individual differences from which psychometrics grew.
https://en.wikipedia.org/wiki/Francis_Galton#Anthropometric_Laboratory1885: Ebbinghaus measures memory and forgetting
In "On Memory", Hermann Ebbinghaus reported years of experiments with himself as sole subject, memorizing lists of nonsense syllables and measuring the time saved when relearning them after delays. He found that forgetting is rapid at first and then levels off, the forgetting curve, and that practice spaced over time works better than massed practice; a one-subject replication published in 2015 produced a similar curve.
https://en.wikipedia.org/wiki/Hermann_Ebbinghaus1890: William James publishes "The Principles of Psychology"
Twelve years in the writing, William James's two-volume work described thought as a continuous "stream of consciousness", made habit central and argued, as the Danish physician Carl Lange did independently, that emotions follow bodily changes rather than cause them. Its view of the mind as purposive and selective made the Harvard professor a founder of functionalism.
https://en.wikipedia.org/wiki/The_Principles_of_Psychology1892: American Psychological Association founded
Meeting at Clark University in Worcester, Massachusetts, on July 8 at the invitation of G. Stanley Hall, holder of the first American doctorate in psychology, a small group founded the American Psychological Association (APA) with Hall as president. As clinicians came to outnumber researchers in the APA, research psychologists founded what is now the Association for Psychological Science in 1988.
https://en.wikipedia.org/wiki/American_Psychological_Association1896: Witmer opens a psychological clinic in Philadelphia
Lightner Witmer, who had earned his doctorate under Wilhelm Wundt, began the work of a "psychological clinic" at the University of Pennsylvania in March with a schoolboy who struggled to spell, then examined and trained children brought by teachers and parents. Generally credited as the first such clinic, it led him to name the field "clinical psychology" in 1907.
https://en.wikipedia.org/wiki/Lightner_Witmer1899: Freud publishes "The Interpretation of Dreams"
Published in Vienna late in the year but dated 1900, Sigmund Freud's book argued that dreams disguise the fulfillment of unconscious wishes and set out the model of the mind behind psychoanalysis. Its first 600 copies took eight years to sell, but psychodynamic ideas came to predominate in American psychiatry until the 1970s, while critics such as the philosopher Karl Popper argued that its claims could not be tested.
https://en.wikipedia.org/wiki/The_Interpretation_of_Dreams1903: Pavlov presents the conditioned reflex in Madrid
Ivan Pavlov, a St. Petersburg physiologist who won the 1904 Nobel Prize in Physiology or Medicine for research on digestion, told a medical congress in Madrid that dogs learn to salivate at signals that regularly precede food. His laboratory used metronomes, whistles and lights as signals. Edwin Twitmyer had reported a conditioned knee jerk in people in 1902, but Pavlov's work made classical conditioning central to the study of learning.
https://en.wikipedia.org/wiki/Ivan_Pavlov1905: Binet and Simon publish an intelligence scale
Prompted by a French government commission on schoolchildren who struggled in ordinary classes, Alfred Binet and Théodore Simon published 30 short tasks of rising difficulty to identify children needing special teaching; their 1908 revision graded the tasks by age. William Stern proposed the intelligence quotient (IQ) in 1912, and Lewis Terman's 1916 Stanford revision spread testing across the United States, where eugenicists used it to argue for sterilization and immigration limits.
https://en.wikipedia.org/wiki/Binet%E2%80%93Simon_Intelligence_Test1912: Wertheimer's motion experiments launch Gestalt psychology
In Frankfurt, Max Wertheimer reported that two lines flashed in quick succession can produce an impression of movement with no moving object seen, the phi phenomenon, using Wolfgang Köhler and Kurt Koffka as his observers. The three founded Gestalt psychology, which held that perception is organized into structured wholes rather than built up from elementary sensations. Nazi rule later drove Wertheimer and Köhler to the United States.
https://en.wikipedia.org/wiki/Gestalt_psychology1913: Watson issues the behaviorist manifesto
In a lecture at Columbia University and an article in Psychological Review, John B. Watson declared that psychology should be "a purely objective experimental branch of natural science" aiming at "the prediction and control of behavior", without introspection. Behaviorism dominated American psychology until the cognitive revolution; in 1920 Watson and Rosalie Rayner conditioned an infant, "Little Albert", to fear a white rat.
https://en.wikipedia.org/wiki/John_B._Watson1923: Piaget begins publishing on how children think
Jean Piaget, who had noticed while scoring intelligence tests in Paris that children of the same age made the same kinds of mistakes, published "The Language and Thought of the Child" while at the Rousseau Institute in Geneva, and went on to propose four stages of thinking, from the sensorimotor intelligence of infants to the abstract reasoning of adolescents. The Soviet psychologist Lev Vygotsky's "Thinking and Speech" (1934) stressed instead social interaction and language.
https://en.wikipedia.org/wiki/Piaget%27s_theory_of_cognitive_development1938: Skinner publishes "The Behavior of Organisms"
In his first book, B. F. Skinner distinguished reflexes elicited by stimuli, as in Ivan Pavlov's conditioning, from "operant" behavior shaped by its consequences, extending the law of effect Edward Thorndike drew from his 1898 puzzle-box studies of cats. Skinner measured how often rats pressed a lever for food in a chamber later called the "Skinner box", founding the experimental analysis of behavior.
https://en.wikipedia.org/wiki/The_Behavior_of_Organisms1942: Rogers proposes nondirective counseling
In "Counseling and Psychotherapy", Carl Rogers argued that a counselor should accept and reflect a client's feelings rather than diagnose or advise. Renamed client-centered and later person-centered therapy, it made Rogers a founder of psychotherapy research based on recorded sessions; with Abraham Maslow, whose 1943 hierarchy of needs was only later drawn as a pyramid by others, he led humanistic psychology.
https://en.wikipedia.org/wiki/Person-centered_therapy1949: Boulder conference adopts the scientist–practitioner model
Meeting in Boulder, Colorado, as federal agencies paid to train psychologists to treat World War II veterans, a conference endorsed David Shakow's plan to train clinical psychologists as both researchers and practitioners, through a doctorate with a supervised internship. The "Boulder model" became the norm for clinical doctoral programs; a 1973 conference in Vail, Colorado, endorsed the practice-oriented Doctor of Psychology (PsyD).
https://en.wikipedia.org/wiki/Scientist%E2%80%93practitioner_model1952: American Psychiatric Association publishes the first DSM
Adapted from a US Army classification of 1945 and aligned with the World Health Organization's sixth International Classification of Diseases, the first "Diagnostic and Statistical Manual of Mental Disorders" (DSM) gave American clinicians a shared glossary of diagnoses. It reflected the psychodynamic psychiatry of the day, described many conditions as "reactions" and listed homosexuality as a mental disorder.
https://en.wikipedia.org/wiki/Diagnostic_and_Statistical_Manual_of_Mental_Disorders#DSM-I_(1952)1956: Miller and Chomsky help launch the cognitive revolution
George Miller later dated the birth of cognitive science to September 11, at a symposium at the Massachusetts Institute of Technology where Allen Newell and Herbert Simon presented a "logic machine", Noam Chomsky outlined transformational grammar and Miller, author of "The Magical Number Seven, Plus or Minus Two", spoke on the limits of short-term memory. Treating the mind as an information processor, cognitive psychology overtook behaviorism by the early 1970s.
https://en.wikipedia.org/wiki/Cognitive_revolution1957: Scoville and Milner report patient H.M.'s amnesia
William Scoville and Brenda Milner reported that Henry Molaison, known as H.M., could no longer form lasting new memories after Scoville removed much of both medial temporal lobes, including large parts of both hippocampi, in 1953 to control his epilepsy, though his intelligence and short-term memory were spared. His case, studied until his death in 2008, helped show that memory consists of separable systems.
https://en.wikipedia.org/wiki/Henry_Molaison1963: Milgram reports his obedience experiments
In the first report of experiments Stanley Milgram began at Yale University in 1961, 26 of 40 men obeyed an experimenter's orders to give what they believed were ever stronger electric shocks to a protesting actor, up to the maximum of 450 volts. The study fueled debate over research ethics, and later study of Milgram's archives by Gina Perry and others questioned how many participants believed the shocks were real.
https://en.wikipedia.org/wiki/Milgram_experiment1963: Beck proposes a cognitive theory of depression
In "Thinking and Depression", the University of Pennsylvania psychiatrist Aaron Beck described recurring, distorted negative thoughts in depressed patients and argued that such thinking sustains depression. His cognitive therapy, which teaches patients to test these thoughts, merged with behavior therapy into cognitive behavioral therapy (CBT); Albert Ellis had developed a similar approach in the 1950s.
https://en.wikipedia.org/wiki/Cognitive_therapy1973: Homosexuality removed from the DSM
In December the American Psychiatric Association's trustees voted to drop homosexuality from the "Diagnostic and Statistical Manual of Mental Disorders" (DSM), after gay activists' protests from 1970 and research such as the psychologist Evelyn Hooker's 1957 study finding gay men no more disturbed than heterosexual men. Members upheld the change in 1974 by 58%; a narrower diagnosis of distress over orientation lasted until 1987.
https://en.wikipedia.org/wiki/Homosexuality_in_the_DSM1974: Tversky and Kahneman describe heuristics and biases
In the journal Science, the Israeli psychologists Amos Tversky and Daniel Kahneman argued that people judge likelihood with a few mental shortcuts (representativeness, availability, and anchoring and adjustment) that usually help but cause systematic, predictable errors. With their prospect theory of 1979 the work helped launch behavioral economics; Kahneman shared the 2002 Nobel Memorial Prize in Economic Sciences, Tversky having died in 1996.
https://en.wikipedia.org/wiki/Heuristic_(psychology)1980: DSM-III introduces explicit diagnostic criteria
Prepared under the psychiatrist Robert Spitzer after studies showed that clinicians often disagreed on diagnoses, the third "Diagnostic and Statistical Manual of Mental Disorders" (DSM-III) gave explicit criteria for each disorder, a multiaxial assessment and an approach neutral about causes. Breaking with the psychoanalytic framing of earlier editions, it came into wide international use.
https://en.wikipedia.org/wiki/Diagnostic_and_Statistical_Manual_of_Mental_Disorders#DSM-III_(1980)2011: Fraud and a precognition study shake psychology
The Journal of Personality and Social Psychology published Daryl Bem's claimed evidence of precognition, which others failed to repeat, and Tilburg University suspended the social psychologist Diederik Stapel for fabricating data; 58 of his papers were eventually retracted. Joseph Simmons, Leif Nelson and Uri Simonsohn then showed that undisclosed flexibility in collecting and analyzing data can make almost any hypothesis look statistically significant.
https://en.wikipedia.org/wiki/Replication_crisis2013: American Psychiatric Association publishes DSM-5
The fifth "Diagnostic and Statistical Manual of Mental Disorders" (DSM-5) dropped the multiaxial assessment system and merged Asperger's disorder into autism spectrum disorder. The National Institute of Mental Health promoted research beyond diagnostic categories while affirming the manual's clinical role. A 2022 text revision added prolonged grief disorder, also included in the World Health Organization's eleventh International Classification of Diseases.
https://en.wikipedia.org/wiki/DSM-52015: Reproducibility Project repeats 100 psychology studies
The Open Science Collaboration, coordinated by Brian Nosek's Center for Open Science, reported in Science on repeating 100 studies published in 2008 in three psychology journals. Although 97% of the originals had reported statistically significant results, 36% of the replications did, with effects averaging half the original size; Many Labs 2 reported in 2018 that half of 28 findings failed to replicate in labs around the world.
https://en.wikipedia.org/wiki/Reproducibility_Project2026: SCORE program finds about half of claims replicate
In Nature, the Systematizing Confidence in Open Research and Evidence (SCORE) program, funded by the US Defense Advanced Research Projects Agency and coordinated by the Center for Open Science, reported high-powered replications of 274 claims from 164 papers published in 2009 – 2018 in psychology, economics and other social sciences. Statistically significant results in the original direction appeared for 55% of the claims and about 49% after weighting by paper, with median effect sizes less than half those originally reported.
https://en.wikipedia.org/wiki/Replication_crisis