What Is Psychology?

Psychology is the scientific study of the mind and behavior, according to the American Psychological Association. Psychology is a multifaceted discipline and includes many sub-fields of study, such as human development, sports, health, clinical, social behavior and cognitive processes.

Psychology is a new science, with most advances happening over the past 150 years.  However, its origins trace back to ancient Greece, roughly 500–300 BC.

The emphasis was philosophical. Socrates (470 BC – 399 BC) influenced Plato (428/427 BC – 348/347 BC), who in turn influenced Aristotle (384 BC – 322 BC).

Philosophers used to discuss many topics now studied by modern psychology, such as memory, free will vs. determinism, nature vs. nurture, attraction, etc.

Over time, as understanding of the mind has grown, specialized areas have emerged. These branches of psychology include clinical, social and developmental psychology.

Definition of Psychology

Meaning and Official Definitions

The word psychology comes from the Greek psyche (mind, soul or spirit) and logos (knowledge or study). Literally, it means the “study of the mind.”

In practice, working definitions have moved well beyond that root. Two widely used ones pair a method with a subject matter:

• American Psychological Association: “the scientific study of the mind and behavior.”
• British Psychological Society: “the scientific study of people, the mind and behaviour.”

Each defines psychology by how it investigates as well as by what it investigates. That is why the question of whether psychology is a science is never far from the question of what psychology is.

Neither is the only definition in circulation. That is a recurring feature of the discipline, not sloppy scholarship.

How and Why the Definition Has Changed

Definitions of psychology have changed often because theorists disagree about what people are like and how best to study them. Two features make a single stable definition hard to settle on:

• Rival images of the person: Approaches picture people as conditioned organisms, information processors, creatures of unconscious conflict or self-actualizing agents, so each studies different things.
• A reflexive subject: Psychologists use memory, inference and social judgment to study those same processes, so the discipline and its subject overlap unusually closely.

The table below traces how the working definition has shifted. Each change altered what counted as legitimate evidence, not only which topics counted.

Era	Definition or focus	Key figure
1879	The study of the mind through trained introspection (structuralism)	Wundt
1890	“the Science of Mental Life, both of its phenomena and of their conditions”	James (1890)
1913	The science of observable behavior only, with introspection rejected (behaviorism)	Watson (1913)
1956	The study of behavior and cognitive processes, with the mind readmitted as subject matter	The cognitive revolution
2015	A discipline reckoning with reproducibility and with how representative its evidence is	Open Science Collaboration (2015)

Wundt accepted trained introspective reports. Watson rejected them in favor of observable behavior. The cognitive revolution readmitted the mind, but only where inferences could be anchored to measurable behavior, such as a reaction time or an error rate.

Psychology Versus Common Sense

Everyone is, in a loose sense, a psychologist. Joynson (1974) framed the puzzle sharply: “If the Psychologist did not exist, would it be necessary to invent him?”

Legge (1975) resolved it by separating formal, scientific psychology from informal, common-sense psychology, rather than treating them as rivals.

Common sense is unsystematic and cannot check itself. Proverbs even contradict one another: “birds of a feather flock together” against “opposites attract.” Formal psychology builds a public, checkable body of knowledge and identifies the conditions under which each claim holds. That illuminates everyday understanding rather than simply negating it.

Everyday words also change meaning inside psychology. Behavior and personality are cases in point. No one is ever “not behaving,” and no one has “no personality,” only a particular one.

The Beginnings of Psychology as a Discipline

In the early days of psychology, two theoretical perspectives dominated debate about how the mind worked: structuralism and functionalism.

Structuralism: Wundt and Introspection

Structuralism was the approach pioneered by Wilhelm Wundt (1832-1920). It focused on breaking mental processes down into their most basic components, much as a chemist analyzes a compound into its elements.

The term originated from Edward Titchener, an American psychologist who had been trained by Wundt.

Wundt separated psychology from philosophy by analyzing the workings of the mind in a more structured way. The emphasis was on objective measurement and control.

Structuralism relied on trained introspection. This research method had participants describe what was going on in their minds while performing a task.

Introspection proved unreliable, because participants’ experiences and reports varied too much. Even so, Wundt remains a key figure. In 1879 he opened the first laboratory dedicated to psychology, an event usually seen as the beginning of modern experimental psychology.

Functionalism: William James

An American psychologist, William James (1842-1910), developed functionalism. This approach disagreed with the focus of structuralism.

James argued that the mind is constantly changing, so it is pointless to look for a fixed structure of conscious experience.

Instead, he asked how and why an organism acts. The question was what function or purpose a mental process serves for survival and adaptation.

James (1890) defined psychology as “the Science of Mental Life, both of its phenomena and of their conditions.”

The two schools disagreed about more than technique. They disagreed about what would count as a satisfactory answer to “what is a thought?” Wundt’s answer was a fixed inventory of elements. James’s answer was an account of function and purpose.

James suggested that psychologists should look for the underlying causes of behavior and the mental processes involved. This emphasis on causes and consequences has influenced contemporary psychology far more durably than structuralism did.

The Perspectives of Psychology

Structuralism and functionalism have since given way to several influential approaches to psychology. Each rests on shared assumptions about what people are like, what is important to study, and how to study it.

To Describe

Describing a behavior or cognition is the first goal of psychology. This can enable researchers to develop general laws of human behavior.

For example, Ivan Pavlov described how dogs’ salivary responses to a bell paired with food changed over repeated trials. That description became the laws of classical conditioning.

To Explain

Once researchers have described general laws of behavior, the next step is to explain how or why this trend occurs. Psychologists propose theories that account for why a behavior happens, rather than merely documenting that it happens.

To Predict

Psychology aims to predict future behavior from the findings of empirical research. If a prediction is not confirmed, the explanation it rests on might need to be revised.

For example, classical conditioning predicts that if a person associates a negative outcome with a stimulus, they may develop a phobia or aversion to it.

This is the logic of falsifiability. A good theory makes predictions that evidence could prove wrong. See Is Psychology a Science?

To Change

Once psychology has described, explained and made predictions about behavior, changing or controlling a behavior can be attempted.

For example, interventions based on classical conditioning, such as systematic desensitization, have been used to treat people with anxiety disorders, including phobias.

The four goals build on one another. Basic research supplies description and explanation, while applied psychology supplies prediction-driven intervention, so one researcher often works across both.

• Aim: To measure how representative the samples in a leading psychology journal are of the world’s population, and to propose reforms.
• Method: The authors coded 223 articles (450 samples) from one year of Psychological Science for sample country and demographic reporting. A follow-up checked 40 later articles.
• Results: 57.76% of samples came from the United States, 71.25% from English-speaking countries and 94.15% from Western nations. Those nations hold about 12% of the world’s population, yet 72% of sampled abstracts reported no demographic details.
• Conclusion: The flagship evidence base comes from a narrow slice of humanity, and papers rarely acknowledge it. The authors proposed mandatory demographic reporting and explicit justification of sampling choices.