Historical Development of the Science of Psychology: From Philosophical Foundations to Modern Theories
Historical Development of the Science of Psychology: From Philosophical Foundations to Modern Theories
(citation: Kuzu, M. E. (2025). Historical Development of Psychological Science: From Philosophical Foundations to Modern Theories)
1.Introduction
1.1 Definition and Importance of Psychology
Psychology is a branch of science that studies and analyzes animal and human behavior and the reasons underlying these behaviors with scientific methods. Derived from the Greek words “psyche” (soul/mind) and “logos” (word/science), this discipline is essentially a scientific reflection of the effort to understand human beings.
1.2 Purpose and Scope of the Article
In order to understand psychology and human behavior in depth, it is essential to know its history, as it is almost impossible to grasp the “now” and the ‘then’ without understanding the “before”. The aim of this article is to briefly summarize the foundations of the history of psychology and to present the movements, intellectual orientations and theoretical transformations that developed in this process in an organized manner.
Our article aims to summarize a broad historical line starting from the “philosopher-psychologists” of Ancient Greece to the “modern psychologists” of today, to examine the important breaking points along this line and to analyze the intellectual evolution.
- Philosophical foundations of psychology
2.1 Understanding of Man and Mind in Antiquity
Although psychology took shape as a scientific discipline in the modern sense in the 19th century, the fundamental questions in this field go back much further, to the birth of philosophy. Ancient Greek philosophers produced various ideas aimed at understanding human behavior and mental processes; these intellectual efforts formed the foundations of psychology.
2.1.1 According to Plato, the soul
Plato (427-347 BC) is the person who put forward the earliest and perhaps the most influential theories on the philosophical foundations of psychology for his time. Here we will briefly summarize his thoughts on the soul.
Plato defines the human mind as a structure consisting of three parts: reason (logistikon), will/anger (thymos) and desire (epithymia).
Intellect (logistikon): The “highest” level of the soul, which functions as wisdom, thinking and cognition. The intellect has to supervise and balance the other two parts
Will/anger (thymos): The intermediate part of the soul that directs the functions of courage, anger, honor and determination.
Desire (epithymia): The lowest part of the soul that governs bodily and pleasure-based desires such as eating, drinking, sexuality and comfort.
According to Plato, the soul is immortal, while the body is temporary. Therefore, the body is like a “prison” where the soul is temporarily housed, and the soul is like a “prisoner” counting the days in prison.
2.1.2. According to Aristotle, the soul
Although Aristotle (384-322 BC) was a student of Plato, he was significantly critical of his understanding of the soul and developed a more biological and functional concept of the mind. Contrary to Plato, Aristotle thinks that the soul is not separate from the body but has a unified structure, and that the soul determines the function of the body.
At the same time, Aristotle, unlike Plato, does not think that the soul is composed of “parts” and believes that the soul is not composed of different parts, but of different “faculties” (dynameis).
these faculties are as follows:
Plant Spirit (Nefs-i Nebâtî): The most primitive level of soul that governs basic biological functions such as growth, nutrition and reproduction. All plants have this type of soul.
Animal Soul (Nafs-i Animal): Includes functions such as sensory perceptions, movement and desires. Both animals and humans have this level.
Rational Soul (Nafs-i Nâtık): It is the highest level that includes functions such as thinking, reasoning and conscious decision-making. It is found only in humans.
Compared to Plato, Aristotle saw the body as a vehicle through which the soul expressed itself. He also introduced the importance of experience and observation and the unity of soul and body (the monism approach) into modern psychological literature.
2.2 Medieval Philosophy and Psychology
In the Middle Ages, science and psychology did not develop much under the influence of scholastic thought. Most of the ideas about the soul were based on religious foundations. In this period, psychology was treated as a field intertwined with philosophy and theology rather than being a direct scientific discipline. The human soul was evaluated in the context of the relationship between nature and God; questions such as the nature, existence and function of the soul constituted the main topics of discussion of the period.
Thomas of Aquinas, representing Christianity, and Ibn Sina, representing the Islamic world, were two prominent thinkers in this period.
2.2.1 Thomas of Aquinas,
Thomas of Aquinas (1225-1274) is considered one of the most important representatives of Christian scholastic thought. He was a philosopher who synthesized Aristotle's ideas with Christian beliefs.
According to Aquinas, the “soul” is the essence that makes man human. Like Aristotle, he argues that the soul is a form of the body. According to him, both a soul without a body and a body without a soul are incomplete; the human being is only complete with the unity of these two.
Thomas of Aquinas also explains the soul in terms of three basic faculties:
Mental faculty (intellectus): The power of knowing and thinking
Will (voluntas): The ability to want and choose
Sensory faculty (sensibilitas): Capacity to feel and perceive
Aquinas tried to explain mental processes such as will, reason and emotion in a systematic way; he had an important place in the history of psychology, especially by laying the philosophical foundations of the concept of conscience.
2.2.2. Avicenna
Avicenna (980-1037) was an Islamic philosopher, physician and scholar. Like Thomas of Aquinas, he adapted Aristotle's philosophy to his own religious and cultural context and created an original synthesis, even giving the regions where the soul is located. According to Avicenna, the soul is considered in three different types:
Natural Spirit (Vegetative Spirit): It resides in the liver and governs basic vital functions such as nutrition, growth and reproduction.
Animal Spirit: It resides in the heart and gives vitality to the body; senses, emotions, and motor skills function through this spirit.
Nephsanic Spirit (Human Spirit): Located in the brain, spinal cord and nervous system; higher mental functions such as cognition, thinking and will are realized through the activities of this soul.
This tripartite classification systematizes the different functions of the soul and its relationship with the body.
Avicenna adopts the classical view on the immortality of the soul; however, he makes an important distinction here. According to him, the vegetable and animal souls perish along with the body because they depend on the basic vital functions of the body. However, the human soul (nafsani soul) is immaterial and continues to exist after the death of the body. In this respect, the human soul is immortal, but not the vegetable and animal soul. ibni sina was the first philosopher to look for the soul in the body.
2.3. Dualism and Monism Debates
The nature of mind and body plays an important role in the philosophical foundations of psychology. René Descartes' dualism emphasized the independence of mental processes in psychology by arguing that the mind and body are two separate entities. On the other hand, Spinoza and later monist approaches paved the way for the integration of psychology and biology by arguing that the mind and body are different aspects of the same being. These debates played an important role and were influential in the establishment of psychology on modern scientific foundations and especially in the birth of disciplines such as neuropsychology.
The monolithism that prevailed with the Renaissance played a crucial role in the acceptance of psychology as an “observable science”.
- The Rebirth of Psychology as a Scientific Discipline
3.1 The Renaissance Rebirth and the Independence of Psychology
The Renaissance was not only a “rebirth” in the arts but also a profound revival in intellectual thought. The dogmatic framework rooted in scholasticism gave way to individual reasoning, observation, and inquiry. With this transformation, theological approaches based on the “divine essence of the soul” were replaced by scientific approaches focusing on the “functioning of the mind.”
Empiricism, pioneered by Francis Bacon, argued that knowledge can only be attained through sensory experience; John Locke, on the other hand, conceptualized the mind as a “blank slate” (tabula rasa), asserting that experiences shape the mind.
These perspectives were pivotal in freeing psychology from metaphysical debates and establishing it as a field grounded in experiment and observation.
Thus, psychology was reborn for the first time with an empiricist outlook, disentangling itself from theology and philosophy. This intellectual foundation laid the groundwork for the scientific accumulation that would culminate in Wilhelm Wundt’s establishment of the first psychology laboratory in 1879.
3.2 Wilhelm Wundt and the First Psychology Laboratory
Wilhelm Wundt (August 16, 1832 – August 31, 1920) was a German physiologist, psychologist, philosopher, professor, and physician. He is regarded as one of the founding figures of modern psychology. His most significant contribution was establishing psychology as an independent scientific discipline. In 1879, he founded the first psychology laboratory and introduced experimental psychology to the scientific world. He also published the first academic journal dedicated to psychology.
Wundt’s groundbreaking methodological innovation of the time was the technique of introspection, which involved individuals carefully observing and describing their own mental experiences. However, this method was later heavily criticized for its subjective nature.
The laboratory he established at the University of Leipzig became a pivotal center for conducting experiments on mental processes such as sensation, perception, attention, timing, and reaction time. Through these efforts, Wundt transformed psychology from a branch of philosophical inquiry into a systematic science based on experimentation and observation, laying the foundation for modern psychology.
3.3 The Experimental Era of Psychology and Its Methodology
The movement of experimental psychology, initiated by Wilhelm Wundt, continued to evolve throughout the 19th and 20th centuries. During this period, psychologists developed various experimental methods and techniques in an effort to establish psychology as an empiricist and objective science.
In this process, the ‘observable’ aspects of behaviours came to the fore and scientific instruments were integrated into psychology.
In this period, measures such as statistics and scientific observation became widespread and significant progress was made in the field of psychometrics.
These methodological developments brought psychology closer to the natural sciences and laid the groundwork for the emergence of applied fields such as clinical psychology, educational psychology, and industrial-organizational psychology. Additionally, this era witnessed the rise of diverse psychological schools of thought, contributing to a growing theoretical pluralism within the discipline.
- Main Currents and Theoretical Development of Psychology
4.1 Structuralism
The first psychological movement that emerged after psychology became a scientific discipline was structuralism pioneered by Wundt (1832-1920).
The basic assumptions of structuralism are as follows:
The mind is made up of analyzable parts.
Understanding these parts leads to an understanding of the mind as a whole.
The introspective method is a valid scientific method for observing mental processes.
it is necessary to analyze the case “piece by piece” and not as a “whole”.
The most important representatives of the structuralist approach in psychology are W. Wundt and Titchener.
However, structuralism was criticized over time due to the subjective nature of the introspective method and these criticisms paved the way for the rise of behaviorism.
4.2 Functionalism
Functionalism is a psychological movement that emerged in the United States in the late 19th century as a reaction to structuralism. Its founder was the American philosopher and psychologist William James (January 11, 1842 - August 26, 1910).
Functionalists drew attention to the subjective nature of the introspective method adopted by structuralists and argued that this method did not add much value to psychology. According to them, psychology should be concerned not only with “what the mind is” but also with “what it does”. For this reason, more emphasis was placed on empiricism, biology and evolutionary theory, and the evolutionary basis of human behavior was emphasized.
Functionalism basically advocated the following:
Mental processes and behaviors exist for the individual to adapt to the environment.
Consciousness is a continuous process, not an intermittent one.
Psychology should investigate not only the contents of the mind, but what these processes do.
The interaction between the organism and its environment must be studied.
Psychology should be an applied science that is relevant to everyday life.
Due to its inability to provide clear definitions and theoretical boundaries, functionalism has remained a general approach tendency rather than a “school”. Nevertheless, the fact that it paved the way for behaviorism theory and the development of applied psychology fields shows that functionalism has an undisputed importance in the history of psychology.
4.3 Behaviorism
Behaviorism is a psychological theory proposed by John Broadus Watson (January 9, 1878 - September 25, 1958) as a reaction to functionalism and structuralism.
According to behaviorists, the only things that can be observed with objective techniques are the reactions of people to environmental stimuli.
The basic principles of behaviorism are the following:
Psychological research should be classified only by observable and measurable behavior
Internal mental processes such as consciousness, emotion and thought are considered outside the scientific method.
Behavioral change can be achieved through environmental stimuli, especially through reinforcement and punishment techniques.
Although behaviorism has been criticized by other schools of psychology for neglecting the internal processes of the human mind, it has made significant contributions to the institutionalization of psychology as a scientific discipline and the establishment of experimental methods.
4.4 Gestalt Psychology
Born in early 20th century Germany, Gestalt Psychology is an important school developed to explain human perception and advocates a holistic approach to mental processes. Gestalt Psychology was born as a reaction to structuralism's approach of "understanding the mind by breaking it down into its parts". Max Wertheimer's “phi phenomenon” experiments constitute the beginning of this school. Gestalt psychologist Kurt Koffka summarized this approach as follows:
“The whole is something other than the sum of its constituent parts.”
According to this school, human beings do not understand the stimuli coming from the environment one by one, but as a whole. Therefore, the lines, dots and shapes that make up a picture are perceived as a whole, not separately. This holistic perception process is called perceptual organization.
Gestalt psychologists have developed a number of different “principles of perception” to understand this perceptual organization. The main Gestalt principles of perception are as follows;
Proximity: Objects close to each other are perceived as a “whole”
Similarity: Objects that are similar in color, shape or size are grouped together.
Continuity: The mind prefers continuous and smooth lines or patterns.
Closure: The mind creates a whole by completing missing information.
Figure-Ground Distinction (Figure-Ground): The mind distinguishes an object as figure (foreground) and perceives the rest as background.
Wolfgang Köhler's experiments on problem solving and insight also show that Gestalt psychology is a learning
4.5 Psychoanalysis (Freud and his followers)
Psychoanalytic theory was developed by the Austrian neurologist Sigmund Freud (1856-1939) in the early 20th century and pioneered a new era in the history of psychology. This theory emphasized the decisive role of unconscious processes on human behavior and focused on the conflicts in the inner world of the individual, repressed emotions and childhood experiences.
The basic assumptions of psychoanalytic theory are as follows:
The mind consists of three layers according to the level of consciousness:
1: consciousness: thoughts, sensations and emotions that the individual is currently aware of,
2: preconsciousness: contents that are not currently recognized but can be brought to consciousness if desired
3: unconscious: The unconscious contains thoughts, desires, impulses and memories that have been repressed, forgotten or hidden by defense mechanisms.
The psychic structure consists of three systems:
1: id: It is innate and works according to the pleasure principle. Instincts such as openness, sexuality, aggression take place in the structure of the id.
2: ego: Working in line with the principle of reality, the ego tries to reconcile the impulses of the id with the conditions of the external world. It enables the person to act in a logical and planned manner.
3: super ego: represents the moral values, social norms and parental teachings internalized by the individual
psychoanalysis has made very important breakthroughs in the field of chronic psychology and played a very important role in the development of psychology by introducing concepts such as the subconscious
Following Freud, names such as Carl Jung, Alfred Adler, Karen Horney have developed and expanded the psychoanalytic tradition from different perspectives. These names criticized the classical Freudian approach in some aspects and put forward more diverse and culturally sensitive theoretical approaches. These developments show that psychoanalysis is not limited to Freud but is a living and transforming theory.
(The basic conceptual framework of psychoanalytic theory, as summarized above, is defined by the stratification of the structure of the mind according to the level of consciousness and the psychic structure functioning in a three-system structure. Other important components of the theory include the stages of psychosexual development and defense mechanisms. )
4.6 Cognitive Revolution and Cognitive Psychology
The cognitive revolution emerged in the 1950s as a reaction to behaviorism's approach that completely excluded mental processes and initiated a paradigmatic transformation in psychology. With this revolution, the human mind, which had been neglected for a long time, was brought back to the center of psychological research.
Cognitive psychology considers the human mind as an "information processing system"; it refers to an active mental structure that perceives, interprets and processes data from the environment and produces behavior as a result of these processes.
The basic assumptions of cognitive psychology are the following:
The mind receives information from the environment, processes it and produces output; these processes cannot be observed but can be modeled scientifically. Behavior is a result of these cognitive processes.
Psychology should focus not only on observable behaviors, but also on the mental mechanisms underlying these behaviors.
Cognitive processes such as perception, attention, memory and language can be studied with scientific methods.
Cognitive psychology has reminded and pioneered psychology that it should also focus on the human mind. With the cognitive revolution, psychology has turned to many new areas of research by focusing on mental processes. This development triggered the emergence of applied fields.
- The Development of Modern Psychology and Its Areas of Application
5.1 The History of Clinical Psychology and Psychotherapyi
Clinical psychology is an applied branch of psychology concerned with the diagnosis, assessment, and treatment of psychological disorders in individuals. Although the birth of modern psychology as a scientific discipline is commonly attributed to Wilhelm Wundt, the historical roots of clinical psychology extend much further back—to ancient times when humans first began to seek understanding of mental disturbances.
5.1.1 Traditional and Religious Approaches
In prehistoric, ancient, and medieval periods, people often attributed neurological or psychological disorders to religious or mythological causes. Explanations for mental illness frequently involved supernatural elements such as possession by spirits or demons. Consequently, treatment methods were developed in accordance with these beliefs, relying on religious, magical, or mythological practices.
Among the treatment methods practiced during this period were:
Trepanning (drilling into the skull): A surgical procedure intended to release evil spirits believed to inhabit the body,
Rituals involving physical suffering: Acts of physical torment designed to weaken the soul’s control over the body,
Shamanic ceremonies and exorcism sessions aimed at expelling malevolent entities from the afflicted individual.
From today’s perspective, these approaches may appear primitive and unscientific. However, such practices are historically significant as they demonstrate humanity’s early recognition of mental disturbances, the need to make sense of them, and attempts to intervene. This reveals that the quest to understand and address psychological disorders is not solely a product of modern science, but rather has deep roots extending back to the earliest cultural and symbolic efforts to interpret human behavior and experience.
5.1.2 The Enlightenment and Scientific Transformation
With the Renaissance, the dogmatic worldview of the Middle Ages gave way to a human- and nature-centered perspective, leading to significant advancements in medicine. In the 18th century, French physician Philippe Pinel opposed the harsh physical restraints imposed on individuals with mental illness. He advocated for freeing patients from their chains and adopting more humane treatment methods.
During this period, psychology began to take shape as an independent discipline grounded in experimental methods. Wilhelm Wundt’s establishment of the first psychology laboratory in the late 19th century marked a turning point, positioning psychology as an experimental science on par with the natural sciences. This shift made it possible to study mental disorders not only from philosophical or religious perspectives but also through systematic observation and experimentation.
This process represents a crucial milestone in laying the scientific foundations of modern clinical psychology.
5.2. The Development of Social Psychology
Social psychology is the scientific discipline that examines how an individual’s thoughts, emotions, and behaviors are influenced by others. This field functions as a theoretical bridge between individual-centered psychological approaches and society-focused sociological perspectives. Its primary aim is to explain how human behavior is shaped within social contexts, how it changes under different circumstances, and what kinds of social factors influence an individual's attitudes, judgments, and decisions within a group.
The historical development of social psychology dates back to the late 19th century, particularly with the work of French thinker Gustave Le Bon on crowd psychology. In his seminal work The Crowd: A Study of the Popular Mind, Le Bon argued that individuals tend to lose rational control when immersed in a crowd, succumbing to the anonymous influence of the group and forfeiting individual reasoning. This perspective marked an important starting point for understanding individual susceptibility to social influence and the dynamics of collective behavior.
By the early 20th century, especially in the United States, social psychology had begun to take shape as a more systematic scientific discipline. Norman Triplett’s 1898 study on bicycle racers and social facilitation is considered the first experimental research in social psychology. Kurt Lewin made significant contributions with his field theory, which posited that behavior results not only from individual characteristics but also from the dynamic interaction between the person and their environment.
World War II had a profound impact on the development of social psychology, spurring increased interest in topics such as propaganda, obedience, group interaction, prejudice, and discrimination. Pioneering studies—such as Solomon Asch’s conformity experiments, Stanley Milgram’s obedience research, and Muzafer Sherif’s investigations into intergroup conflict—enhanced our understanding of how individuals behave under social pressure and within group settings.
During this period, social psychology evolved into a field not only concerned with individual behavior but also committed to understanding broader societal issues. Topics such as discrimination, prejudice, social identity, stereotyping, attitude change, social influence, and group dynamics have since become central areas of inquiry in the discipline.
5.3 Neuropsychology and the Rise of the Cognitive Sciences
Neuropsychology is the branch of psychology that studies the relationship between the brain and behavior. It seeks to understand how damage or differences in function in certain areas of the brain affect cognitive, emotional and behavioral processes. From the mid-20th century onwards, neuropsychology brought a new dimension to psychology, as it was now possible to explain human behavior not only through external observations, but also through the structure and function of the brain.
On the other hand, cognitive sciences brought a breath of fresh air to psychology and experimentally and theoretically modeled the information processing processes of the mind.
In the 1950s, the cognitive revolution emerged in response to behaviorism's focus on observable responses. This revolution made possible the scientific investigation of mental processes. The human mind was considered as an active system that processes information and was modeled with the computer metaphor. In this way, psychology has become a multidisciplinary science by interacting with disciplines such as artificial intelligence, linguistics, neuroscience and philosophy.
- Result
6.1 General Evaluation
The history of psychology is one of the most profound searches in human history to understand the behavior and mental processes of individuals. This process, ranging from ancient philosophy to modern scientific approaches, has made psychology not only a field of study but also an attempt to understand human nature in a multidimensional way.
In this study, the historical development of psychology is analyzed from its philosophical foundations through experimental institutions, main movements and contemporary subfields. Each period has played a critical role in the acquisition of psychology's scientific identity and the expansion of its fields of application.
Psychology continues to be a rapidly developing field with both theoretical and applied aspects and open to interdisciplinary collaborations. In this context, understanding the history of psychology is of great importance not only to know the past, but also to comprehend the intellectual background of today's psychology and to evaluate its future directions.
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