1 Introduction and Learning Objectives

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Learning Objectives.

2 Questions in Psychology

Have you ever asked any of these questions?

These are just some of the questions we seek to answer through the scientific discipline of psychology. Psychology is the scientific study of behavior, cognition, and emotion (or affect). This definition includes both a what and a how. The what—behavior, cognition, and emotion—represents the engaging subject matter that anyone, regardless of training, can theorize about and explore. The difference between any person and a psychologist, however, lies in the how: psychologists use the scientific method (more on this below) to test and refine their ideas.

This guide will begin with an overview of the history of psychology as a scientific discipline, and also the types of questions psychologists ask. Finally, we’ll transition to asking how psychologists use the scientific method to investigate and evaluate their theories.

3 History and Systems

To understand modern psychology, we must begin with its roots in the past. Although psychology did not emerge as a distinct scientific discipline until the late 1800s, many ancient philosophers and early physicians asked questions and sought truths that closely relate to what we now consider the domain of psychology.

Early humans believed that everything in nature was alive—animism. This led to the idea that they could control nature (e.g., the Greeks had gods such as Apollo for the sun and Poseidon for the sea).

Philosophers began to seek natural rather than supernatural explanations for phenomena, including human health and thought. For example, there was an early effort to identify the basic substance from which everything was made. Anaximander (610–540 B.C.) proposed a basic substance of boundless qualities that could become anything (e.g., hot water and earth formed fish). Democritus (460–370 B.C.) proposed the existence of the atom—tiny particles that made up all matter. This idea exemplifies reductionism, the idea that complex phenomena can be explained entirely in terms of simpler ones. It wasn’t long before philosophers began applying reductionist ideas to the basic building blocks of mental processes as well.

3.1 Hippocrates and the Four Humors



Marble bust of Hippocrates, the ancient Greek physician known as the father of modern medicine
Figure 1. Hippocrates, often regarded as the father of modern medicine. Source: Wikimedia Commons.



Hippocrates (460–377 B.C.) is often considered the father of modern medicine. He gathered medical knowledge and promoted a naturalistic view of health and disease. His humoral theory (humor is Latin for fluid) proposed that health depended on a balance of four bodily fluids:

  1. Blood (associated with air) – Thought to be linked to a sanguine temperament: cheerful, optimistic, and passionate.
  2. Yellow bile (associated with fire) – Believed to cause a choleric temperament: irritable, hot-tempered, and aggressive.
  3. Black bile (associated with earth) – Associated with a melancholic temperament: sad, introspective, and prone to depression.
  4. Phlegm (associated with water) – Linked to a phlegmatic temperament: calm, unemotional, and sluggish.


Diagram showing the four humors and their associations with elements and qualities
Figure 2. Diagram of the four humors, showing their associated elements and qualities. Source: Wikimedia Commons.



Each humor was linked to specific emotions and personality traits, and illness was thought to result from an imbalance among them. Treatments aimed to restore balance through diet, lifestyle, or medical interventions like bloodletting.

Hippocrates also de-emphasized religious explanations for illness, famously rejecting the idea that epilepsy was a “sacred disease”, instead attributing it to natural causes.

3.2 Truth, Reason, and the Origins of Knowledge

Early philosophical debates focused on defining truth and reality. Pythagoras (580–500 B.C.), for example, proposed a dualistic universe: 1. A permanent, intellectual world of truth; and 2. A world based on changing sensory experience. He also believed mathematical harmony and balance contributed to health.

The Sophists were professional teachers of rhetoric in ancient Greece who believed that truth was subjective—that it varied from person to person based on their education, culture, experiences, and beliefs. Rather than seeking universal or absolute truths, the Sophists focused on persuasion and argumentation, teaching students how to make effective cases regardless of the underlying truth. This relativistic view challenged traditional philosophical thinking and laid early groundwork for debates about the nature of knowledge, morality, and perception.



Marble bust of Socrates, the ancient Greek philosopher known for his contributions to ethics and epistemology
Figure 3. Bust of Socrates, the ancient Greek philosopher known for the Socratic method. Source: Wikimedia Commons.



Socrates (469–399 B.C.) partially agreed with the sophists’ belief that human experience shapes understanding, but he argued that some universal truths exist and can be discovered through inductive reasoning—a method of drawing general principles from specific observations. For example, by engaging others in dialogue and asking probing questions (i.e., the Socratic method), he believed one could uncover the essence of abstract concepts like beauty, justice, or virtue, which were not dependent on individual opinion but reflected deeper, shared truths.



Marble bust of Plato, the ancient Greek philosopher and student of Socrates, known for his theory of forms and the Allegory of the Cave
Figure 4. Bust of Plato, the ancient Greek philosopher known for his theory of forms and the Allegory of the Cave. Source: Wikimedia Commons.



Plato (427–347 B.C.), a student of Socrates, believed that sensory experiences led to ignorance, and that truth existed in ideal forms (e.g., the Allegory of the Cave). He and Socrates believed that: 1. Knowledge was pre-existing; 2. Learning was achieved through inner exploration; 3. The mind and body were separate (dualism).

🎥 Watch this!
Learn about Plato’s famous Allegory of the Cave at this short YouTube video.



Marble bust of Aristotle, the ancient Greek philosopher and student of Plato, known for his contributions to logic, biology, and empirical observation
Figure 5. Bust of Aristotle, the ancient Greek philosopher known for his emphasis on empirical observation and systematic study. Source: Wikimedia Commons.



Aristotle (384–322 B.C.), a student of Plato, diverged from his mentor by valuing empiricism—the idea that careful observation of nature leads to knowledge. He was the first to write extensively on many ideas that are commonly studied in psychology today including: Memory, Sensation, Sleep, Dreams, Aging, and Learning. Aristotle believed that the human mind begins as a blank slate (tabula rasa), without any built-in ideas or knowledge. He argued that all understanding comes from experience and sensory observation, as the mind is shaped by what it perceives in the world.

3.3 Medieval Thought and the Rise of Empiricism

The so-called Middle Ages saw the dominance of the Roman Catholic Church in Europe. Philosophers turned their focus toward questions of spirituality, religion, and how to live a good life. During this time, middle eastern scholars translated the works of Greek and Roman philosophers, using that wisdom to advance mathematics, medicine, and the sciences.



Painting of Avicenna, the Persian philosopher and physician known for his work in medicine and early psychology
Figure 4. Painting of Avicenna, the Persian philosopher and physician who expanded on Aristotle’s concept of the mind as a blank slate and wrote about mental illness and its treatment. Source: Wikimedia Commons.



Among these figures was Ibn Sīnā (Latinized as Avicenna, 980–1037), who expanded on Aristotle’s concept of the tabula rasa (blank slate) and wrote extensively on mental illness and its treatment.



Painting of Thomas Aquinas, the medieval philosopher and theologian known for integrating reason and religious faith
Figure 5. Painting of Thomas Aquinas, the medieval philosopher and theologian who argued that reason and faith could coexist—a view known as Natural Theology. Source: Wikipedia.



Influenced by both Avicenna and Aristotle, St. Thomas Aquinas (1225–1274) argued that reason and faith could and should coexist—a foundation of what became known as Natural Theology. His synthesis of philosophy and theology strengthened Scholasticism and laid the groundwork for later movements, eventually reducing the Church’s exclusive intellectual control over Europe and paving the way for the Renaissance.

Figures like Copernicus (1473–1543) and Galileo (1564–1642) directly challenged the Church’s view of the universe, while Martin Luther (1483–1546) initiated the Protestant Reformation, reshaping European religious and philosophical thought and paving the way for modern science to flourish.

3.4 Descartes and the Mind-Body Problem



Painting of René Descartes, the French philosopher known for mind-body dualism, who declared 'I think, therefore I am'
Figure 6. Painting of René Descartes, the French philosopher who famously argued for mind-body dualism and declared, “I think, therefore I am.” Source: Wikimedia Commons.



René Descartes (1596–1650) is perhaps the most well-known proponent of dualism, the belief that the mind and body are separate but interact. Famously declaring “I think, therefore I am,” Descartes believed that God implanted a rational, pre-formed mind in every person to help them understand the world. The body, he argued, was merely a machine that reacted to stimuli. While Descartes maintained a spiritual view of the mind, his ideas ultimately laid the groundwork for scientific inquiry into the nervous system and its role in controlling behavior and mental processes.

🧠 Odd fact: After his death in Sweden, René Descartes’ body was exhumed and reburied in France—but not without complications. Over the years, his remains were reportedly disturbed multiple times. His skull was separated from his body and passed through various hands before eventually being placed in the Muséum National d’Histoire Naturelle in Paris. According to some accounts, a French ambassador may have taken a finger as a relic, though this detail remains uncertain.

3.5 British Empiricism



Painting of John Locke, the English philosopher known for his theory of the mind as a blank slate and for advancing empiricism
Figure 7. Painting of John Locke, the English philosopher who expanded on Aristotle’s idea of the mind as a blank slate and promoted empiricism as the basis of knowledge. Source: Wikipedia.



In contrast to Descartes, a group of British philosophers—Thomas Hobbes (1588–1679), John Locke (1632–1704), George Berkeley (1685–1753), and David Hume (1711–1776)—rejected the idea of innate knowledge and subjectivity.

They championed empiricism, the view that all knowledge comes from experience, and that human thought and behavior are reducible to physical and mechanical processes. British Empiricism laid the foundation for modern science and the scientific method by emphasizing observation, measurement, and the accumulation of evidence through the senses.

3.6 Founders and Pioneering Figures of Psychology

The 1800s saw the emergence of psychology as a distinct discipline. Many early thinkers in the field were polymaths who studied numerous topics in the natural sciences and viewed psychology as a natural extension of the work they were already doing.



Portrait of Charles Darwin, the English naturalist known for his theory of evolution by natural selection
Figure 8. Portrait of Charles Darwin, the English naturalist whose theory of evolution laid the foundation for modern understandings of human behavior and the nature vs. nurture debate. Source: Wikimedia Commons.



Charles Darwin (1809–1882) proposed the first scientifically grounded theory of human evolution in On the Origin of Species, laying the groundwork for what would later become the nature vs. nurture debate in psychology (i.e., whether mental traits are shaped more by our biological inheritance [nature] or by our life experiences [nurture]). Following On the Origin of Species (1859) and The Descent of Man (1871), Charles Darwin published The Expression of the Emotions in Man and Animals (1872), in which he argued that basic emotional expressions—such as anger, joy, and disgust—are evolutionarily conserved across species, including humans. His key point was that we inherit our mental traits from our ancestors and adapt them over time to improve our chances of survival.

🎥 Watch this before continuing!

Too Much Emphasis on Nature.


Portrait of Wilhelm Wundt, the German psychologist known as the founder of the first experimental psychology lab
Figure 9. Portrait of Wilhelm Wundt, the German psychologist who founded the first experimental psychology lab and focused on studying the basic elements of conscious experience. Source: Wikimedia Commons.



Wilhelm Wundt (1832–1920), a German physician and former medical student, is widely credited with founding the first psychological laboratory. Influenced by Helmholtz, Wundt focused on identifying the basic elements of thought, which he categorized into sensations and feelings. His approach, known as voluntarism, proposed that humans could willfully focus their attention. Wundt believed that when the mind’s ability to apperceive (actively interpret experience) failed, mental disorders could result.



Portrait of Edward Titchener, the British psychologist who developed structuralism and promoted introspection as a method of studying the mind
Figure 10. Portrait of Edward Titchener, the British psychologist who developed structuralism and promoted introspection to study the structure of conscious experience. Source: Wikimedia Commons.



Edward Titchener (1867–1927), a British psychologist who studied under Wundt, brought his ideas to the United States and developed the theory of structuralism at Cornell University. Structuralism aimed to understand the structure of the mind through introspection, asking participants to describe mental experiences in terms of quality, intensity, duration, clearness, and extensity. However, introspection proved unreliable and did not endure as a scientific method.



Portrait of William James, the American psychologist and philosopher known for founding functionalism and emphasizing the practical purpose of mental processes
Figure 11. Portrait of William James, the American psychologist and philosopher who founded functionalism and emphasized the practical function of thought and behavior. Source: Wikimedia Commons.



William James (1842–1910) marked a key transition in the field, helping to shift the focus of psychology from not just Europe but also the United States. His approach, known as functionalism, emphasized the practical functions of mental processes rather than their contents. James believed in studying only useful and adaptive mental processes and behaviors, criticizing structuralism for being overly abstract. Functionalists embraced pragmatism, leading them to explore areas like animal behavior and eventually contributing to the rise of behaviorism.



Portrait of Sigmund Freud, the Austrian neurologist and founder of psychoanalysis
Figure 12. Portrait of Sigmund Freud, the Austrian neurologist who founded psychoanalysis and developed theories centered on the unconscious mind and early childhood experiences. Source: Wikimedia Commons.



The famed Austrian physician Sigmund Freud (1856–1939) founded psychoanalytic theory, one of the most influential psychological schools of thought. Freud was born to a 40-year-old father and a 20-year-old mother, and he was reportedly his mother’s favorite child—perhaps fueling the roots of his controversial Oedipus complex theory (i.e., which posits that young boys experience unconscious feelings of attachment toward their mothers and rivalry toward their fathers).

Freud developed his ideas while treating patients with hysteria, an antiquated diagnosis rooted in the historical belief that such symptoms were caused by a wandering uterus—a view that originated with Hippocrates. Influenced by figures like Mesmer (see below), Charcot, and Breuer, Freud initially used hypnosis but later turned to techniques like free association, catharsis, and transference. Freud’s work emphasized the power of the unconscious mind, challenging the idea that people are fully in control of their thoughts.

Freud’s students and followers—such as Anna Freud, Carl Jung, Alfred Adler, and Karen Horney—expanded and revised many of his concepts, shaping the evolution of modern psychotherapy.

🧠 Odd fact: Sigmund Freud was an avid user and early promoter of cocaine. In the 1880s, he praised it as a magical drug and recommended it for various ailments, including depression, indigestion, and even as a cure for morphine addiction—before its addictive dangers were fully understood.



Portrait of John B. Watson, the American psychologist who founded behaviorism and emphasized the study of observable behavior
Figure 13. Portrait of John B. Watson, the American psychologist who founded behaviorism and argued that psychology should focus solely on observable behavior and conditioning. Source: Wikimedia Commons.



John B. Watson (1878–1958), an American psychologist, established behaviorism, a movement that rejected introspection and focused entirely on observable behavior. Watson believed that behavior could be shaped entirely through conditioning, famously claiming that he could turn any infant into a doctor or a janitor through proper training. He was strongly influenced by Ivan Pavlov (1849–1936), who discovered classical conditioning, or learning through automatic associations.



Portrait of B.F. Skinner, the American psychologist known for developing operant conditioning and advancing behaviorism
Figure 14. Portrait of B.F. Skinner, the American psychologist who developed the theory of operant conditioning and helped establish behaviorism as a dominant force in psychology. Source: Wikimedia Commons.



B.F. Skinner (1904–1990) later formalized behaviorism through operant conditioning, which focuses on voluntary behaviors shaped by reinforcement and punishment.



Portrait of Carl Rogers, the American psychologist known for developing client-centered therapy and promoting unconditional positive regard
Figure 15. Image of Carl Rogers, the American psychologist who developed client-centered therapy and emphasized the importance of unconditional positive regard in humanistic psychology. Source: Wikimedia Commons.



Abraham Maslow (1908–1970) and Carl Rogers (1902–1987) challenged both psychoanalysis and behaviorism with the development of humanistic psychology. This approach emphasized human potential, free will, and the belief that people are fundamentally good. Maslow introduced the hierarchy of needs, a motivational theory that organizes human desires from basic survival to self-actualization. Rogers promoted unconditional positive regard and client-centered therapy, advocating for genuine, empathetic therapeutic relationships. Together, their work formed the foundation of humanism, a movement aligned with existential philosophy and focused on the whole person rather than pathology or behavior alone.



Photograph of Kenneth B. Clark and Mamie Phipps Clark, African American psychologists known for their research on racial identity and school segregation
Figure 16. Photograph of Kenneth B. Clark and his wife, Mamie Phipps Clark, African American psychologists whose landmark research on racial identity and segregation played a pivotal role in the Supreme Court’s Brown v. Board of Education decision. Source: Flickr.



Kenneth B. Clark (1914–2005) was a pioneering African American psychologist best known for the Doll Studies, conducted with his wife and collaborator, Mamie Phipps Clark (1917–1983). Together, they demonstrated the negative psychological effects of segregation on Black children—findings cited in the landmark Brown v. Board of Education (1954) decision that ended legal school segregation in the U.S. In addition, Mamie Phipps Clark founded the Northside Center for Child Development in Harlem, providing vital psychological services to the community, while Kenneth Clark became the first Black president of the American Psychological Association (APA) and a leading advocate for social justice in psychology.



Portrait of Brenda Milner, the Canadian neuropsychologist known for pioneering work on memory and patient H.M.
Figure 17. Portrait of Brenda Milner, the British-Canadian neuropsychologist whose landmark work with patient H.M. helped establish cognitive neuroscience. Source: The Canadian Encyclopedia.



Brenda Milner (born 1918) is a renowned neuropsychologist widely credited with founding the field of cognitive neuroscience. Her pioneering work with the patient H.M. revealed that the hippocampus plays a critical role in forming new long-term memories, reshaping our understanding of brain function and memory systems.



Portrait of Sandra Bem, the American psychologist and feminist scholar known for the Bem Sex-Role Inventory and psychological androgyny
Figure 18. Portrait of Sandra Bem, the American psychologist and feminist scholar who introduced psychological androgyny and challenged traditional gender roles with the Bem Sex-Role Inventory. Source: Academia.edu.



Sandra Bem (1944–2014) was a pioneering feminist psychologist best known for the development of the Bem Sex Role Inventory (BSRI). Her work introduced the idea of androgyny, proposing that individuals could embody both masculine and feminine traits, and helped shift the understanding of gender roles from rigid binary categories to more fluid and socially constructed dimensions.

Of course, many important figures are not mentioned in this brief lecture. You’ll learn more about modern pioneers and leaders in psychology as the course progresses.

🌐 Explore this! Learn more the History of Psychology Timeline from Annenberg Learner. This interactive timeline provides a concise overview of the key events, influential figures, and foundational ideas that have shaped the field of psychology. It highlights major milestones—from Wilhelm Wundt’s establishment of the first psychology lab to modern developments in cognitive and behavioral science—and illustrates how psychology has evolved as both a science and a profession. As you review it, consider the following question: Which event in the timeline do you believe is most significant to your life, and why?

3.7 Theoretical Frameworks and Sub-Fields in Psychology

Biological psychology (including neuropsychology) examines the physiological mechanisms in the brain and nervous system that organize and control behavior. It focuses on how processes like neural activity, hormones, and genetics influence psychological phenomena.

Psychoanalytic psychology is both a theory of the mind and a method of treatment. It emphasizes the influence of unconscious processes and early childhood experiences on behavior.

Behavioral psychology focuses on how behaviors are learned and modified through conditioning. It emphasizes observable behavior over internal mental processes.

Cognitive psychology studies how knowledge is acquired, organized, stored, and used. It investigates mental processes such as perception, memory, language, and problem-solving.

Humanistic psychology emphasizes personal growth, free will, and self-actualization. It focuses on conscious experience and a more positive view of human nature than traditional psychoanalysis.

Gestalt psychology emphasizes understanding psychological phenomena as structured wholes rather than isolated parts. It argues that breaking experience into elements (as in structuralism or behaviorism) misses the full picture.

Social psychology examines how individuals’ thoughts, feelings, and behaviors are influenced by social environments and group dynamics. Topics include conformity, persuasion, prejudice, and interpersonal relationships.

Personality psychology explores individual differences in patterns of thinking, feeling, and behaving. It focuses on personality traits, temperament, and how personality influences behavior across time and situations.

Developmental psychology studies psychological growth and change across the lifespan. It considers how early experiences, education, and aging affect physical, emotional, and cognitive development.

Cross-cultural psychology investigates how cultural factors shape human behavior and mental processes. It highlights the role of cultural norms, values, and identity in shaping psychological functioning.

Evolutionary psychology applies principles of natural selection to explain psychological traits and behaviors. It explores how certain mental and behavioral adaptations may have evolved to solve survival and reproduction challenges.

Feminist (Gender) psychology examines how gender, power, and social structures shape psychological experience. It challenges androcentric biases in traditional psychology and emphasizes intersectionality, equity, and lived experience.

Clinical psychology focuses on diagnosing and treating mental illness, emotional disturbances, and psychological disorders. Clinical psychologists often work in hospitals, private practices, and community health centers, using a variety of evidence-based therapies and assessments.

Counseling psychology is closely related but tends to focus more on helping individuals cope with life stressors, personal growth, and adjustment issues. Counseling psychologists frequently work in schools, universities, or outpatient clinics and emphasize well-being and resilience.

Industrial-organizational (I/O) psychology applies psychological principles to the workplace to improve productivity, employee satisfaction, and organizational effectiveness. I/O psychologists study topics such as hiring practices, leadership, motivation, performance appraisal, and work-life balance. They often work in businesses, government agencies, or consulting firms to enhance both employee well-being and organizational outcomes.

Positive psychology focuses on the scientific study of human strengths, well-being, and optimal functioning. It emphasizes positive emotions, resilience, meaning, and what helps individuals and communities thrive.

3.8 Where Do Psychologists Work?

🌐 Explore this! Follow this link to an American Psychological Association website where you can learn more about modern careers in psychology.

4 Research Methods

4.1 The Scientific Method and Empiricism

Yes—psychology is a science. But it only earns that designation when it relies on the scientific method to investigate questions and test ideas. The scientific method is more than a fixed series of steps; it’s a philosophical outlook and a set of techniques rooted in observation, measurement, and logical reasoning. The basic principles of the scientific method include:

  1. Empirical support – We accept explanations only when they are supported by evidence. Theories must not only explain behavior but also make testable predictions.

  2. Transparency and replication – Scientific findings must be replicable, and researchers must clearly describe their methods so others can evaluate and reproduce their work.

  3. Self-correction – Science is a self-correcting process. As new evidence emerges, theories are refined or replaced. Psychology, like all sciences, evolves over time.

Psychologists rely heavily on empiricism—the belief that the only path to understanding is through observable, measurable evidence. Empiricism demands that we focus on the objective, not the subjective. Your personal experience—how you feel, what you believe—is subjective. But what can be measured and observed by all is objective.

Experience is not the same as empiricism. Experience is personal; empiricism is systematic. Just because you’ve experienced something doesn’t mean it qualifies as empirical evidence—empiricism requires structured data collection, control of bias, and replication, not just memory or intuition.

“Experience seems to most of us to lead to conclusions, but empiricism has sworn never to draw them.”
— George Santayana

Some of the questions listed at the beginning of this guide, and many others you’ve likely wondered about, may feel deeply personal. Perhaps you’ve experienced a traumatic brain injury, or your great grandfather died in the Holocaust, or you’ve been diagnosed with ADHD. Connecting personally to course content can be motivating and valuable, and we should never trivialize personal experience. But it’s also important to recognize that we all carry subjective opinions that may not be grounded in objective evidence. One of the key learning objectives in this course is to think like a psychologist—to separate personal beliefs from scientifically validated truths.

That said, even science has its limits. The scientific method is constrained by our current tools, technologies, and cognitive capacities. We may struggle to fully comprehend phenomena like the expanding universe, paradoxes, or the nature of time and space. To make such complex ideas more accessible, we often try to simplify them. As Albert Einstein famously remarked, “If you can’t explain it simply, you don’t understand it well enough.”

We shouldn’t let the complexity and enormity of psychology discourage us. We should move forward in science without hesitation and without fear of failure or misunderstanding, but all the while understanding that our theories are usually wrong, even if only in a minor way. As Stephen Hawking once wrote: “Humanity’s deepest desire for knowledge is justification enough for our continuing quest. And our goal is nothing less than a complete description of the universe we live in.”

While our goal in this class is perhaps a bit more modest—understanding the human mind and behavior—it is no less meaningful. In many ways, the mind itself feels as vast and mysterious as the universe.

4.2 Theories and Hypotheses

A theory is like a large-scale map—its broad areas represent general principles, and the connections between them are governed by logical rules. A hypothesis, in contrast, is like a small sectional map focused on a specific area glossed over by the larger map. Hypotheses are more directly amenable to empirical confirmation because they are narrower and more testable.

Both theories and hypotheses should conform to three general principles:

  1. Correspondence with Reality: Ideas should be grounded in reality. However, even widely accepted ideas can turn out to be false (e.g., the belief that the Earth is the center of the universe).

  2. Coherence and Parsimony: According to Occam’s Razor, attributed to 14th-century philosopher William of Occam, “What can be explained with fewer principles is explained needlessly by more.” In science, simpler explanations are generally preferred over more complex ones when both account for the same data.

  3. Falsifiability: Philosopher Karl Popper argued that good science involves coming up with ideas that can be tested and potentially proven wrong. He cautioned against “bucket positivism,” where people collect selective evidence to support almost any claim. A theory that cannot be falsified is not scientifically useful.

Example: Pseudoscience vs. Falsifiable Science: In the 18th century, Franz Mesmer, a physician in Vienna, claimed he could heal people using magnets. Eventually, he believed he could do so through his own animal magnetism. A scientific committee led by Benjamin Franklin, appointed by the King of France, investigated Mesmer’s claims. They found the effects were due to suggestion, not magnetism. Later, hypnotists embraced suggestion as a therapeutic tool, even though the original explanation was debunked. This illustrates that it’s possible to find empirical support for even the most dubious claims—what matters is whether a claim is testable and falsifiable.

In contrast, Einstein’s theory of general relativity offered a bold and risky prediction: during the 1919 solar eclipse, light from stars passing near the sun would appear to bend due to the gravitational warping of space. This prediction was later confirmed through direct observation—an example of a falsifiable and empirically supported hypothesis.

4.3 Types of Research in Psychology

  1. Descriptive Research: Descriptive research involves carefully observing and mapping out a situation in order to describe what is happening behaviorally. It is often the first step in the research process. For example, educational psychologists may study children who perform poorly in school to identify possible causes—such as poor nutrition, inadequate instruction, or cognitive delays.

  2. Correlational Research: Correlational research examines how two variables change together. It asks: as one variable changes, does (or how does) another variable change along with it? Continuing the previous example, researchers might observe that students who are struggling academically receive less attention from their teachers and have fewer opportunities to engage with new academic material.

  3. Experimental Research: Experimental research focuses on identifying cause-and-effect relationships. It seeks to move from “X is related to Y” to “X causes Y.” For instance, researchers could randomly assign students to two groups and have teachers give one group more attention than the other. If the group that received more attention performs better on academic assessments, we may conclude that teacher attention contributes to academic success.

🧠 Related finding: The example above was actually investigated by Rosenthal and Rubin. They found that students’ academic performance improved when they received more attention from their teachers. But what determined which students received more attention? Interestingly, it wasn’t based on ability—it was based on the teacher’s expectations. This phenomenon, where expectations influence outcomes, is known as a self-fulfilling prophecy.

4.4 Correlation ≠ Causation

Relational research often tempts us to make the leap from correlation to causation—but this is a mistake. Assuming a causal relationship without proper experimental controls is an example of ad hoc logic (i.e., reasoning developed specifically to explain a particular result without broader justification) and the post hoc fallacy (i.e., the mistaken belief that because one event follows another, the first must have caused the second). For example, instead of concluding that teacher neglect causes poor student performance, it might actually be that students struggling academically receive less attention (i.e., poor performance causes neglect). (In truth, both explanations are likely correct: neglect can lead to poor performance, and poor performance can lead to neglect.)

Here are some examples of correlation leading to flawed logic:

  • Global warming is strongly correlated with the decline in pirate populations since the 1800s. Does that mean fewer pirates cause global warming?

  • Sleeping with one’s shoes on is strongly correlated with waking up with a headache. Therefore, sleeping with your shoes on causes headaches…

  • From The Simpsons: The “Bear Patrol” Fallacy.

    Springfield creates a high-tech Bear Patrol system after spotting a single bear in an area where bears are uncommon.
    > Homer: Ahh. Not a bear in sight. Bear Patrol must be working like a charm!
    > Lisa: That’s specious reasoning Dad.
    > Homer: Thank you honey.
    > Lisa: By your logic, I could claim this rock keeps tigers away.
    > Homer: Hmm. How does it work?
    > Lisa: It doesn’t. It’s just a stupid rock!
    > Homer: Uh huh.
    > Lisa: But I don’t see any tigers around here. Do you?
    > Homer: Lisa, I want to buy your rock.



Image of a Bear Patrol van from The Simpsons, showing a crossed-out bear symbol. Used in a satirical example of flawed logic, where the absence of bears is incorrectly attributed to the Bear Patrol program.
Figure 20. A scene from The Simpsons illustrating the logical fallacy of assuming causation from correlation. Homer credits the absence of bears to a new Bear Patrol, humorously missing the point that correlation does not imply causation. Source: Simpsons Wiki.



These examples underscore the importance of experimental research when trying to establish causality. Correlation may suggest a relationship, but it does not prove that one variable causes the other.

4.5 Experimental Design

Experiments are used to determine if one variable of interest causes change in another variable of interest.
For example: Does Prozac decrease depressive symptoms?

4.5.1 True Experiments

True experiments are used to explore cause and effect between variables. There are two major types of variables:

  • Independent Variable (IV): The presumed cause. It is manipulated by the researcher.

  • Dependent Variable (DV): The presumed effect or outcome being measured.

Variables can be conceptualized as either independent or dependent. Example: Rumor mongering can incite riots, and riots can incite rumor mongering.

4.5.2 Defining Features of Experiments

  1. Manipulation of the Independent Variable
    The researcher decides which group receives the IV. E.g.,
    • Control Group: A baseline group that does not receive the treatment.
    • Experimental Group: The group that receives the treatment or manipulation.
  2. Control of Confounding Variables
    • Through random assignment: Every participant has an equal chance of being placed in either group.

4.5.3 Confounding Variables

Manipulation and control of the independent variable is critical to avoid the misattribution of cause. In non-experimental research, we always run the risk of confounders.

A confounder variable is a variable that influences both the independent variable (X) and the dependent variable (Y) in a study, creating a spurious or misleading association between them.

In the examples above, the confounding variable creating the spurious association between global warming and the decline in pirates is industrialization, and the confounder linking wearing shoes at night and headaches is alcohol consumption.

Why does manipulation and control of independent variables help us avoid misattributing causes due to confounders? Simple: if assignment to each level of your predictor (e.g., treatment groups) is random, then no group is expected to have more of the confounding variable than another. This prevents the confounder from creating a misleading association between your predictor and outcome.

4.5.4 Quasi-Experiments

So, based on the arguments above, should we always conduct true experiments? Ideally—yes, from a scientific perspective. But in many cases, it is unethical or impractical to randomly assign people to different levels of a predictor (e.g., childhood abuse).

For this reason, in many areas of psychological research, true experiments aren’t possible. In such cases, we rely on what are called quasi-experiments. Quasi-experiments resemble true experiments but lack random assignment. They use a variety of strategies to limit the influence of confounders—for example, through statistical controls or design elements. For example, if we’re interested in comparing health outcomes between people with and without traumatic brain injuries—but recognize that it would be unethical to randomly assign brain injuries—we might instead recruit individuals who already have a brain injury and then match them to individuals without a brain injury who are otherwise similar on key variables (e.g., in age, education, work history, etc.) to eliminate these variables as possible confounders.

4.6 Ethical Questions in Psychology

As suggested by the previous discussion, psychological science raises several important ethical questions, including:

  1. Human and Animal Experimentation: Is it ethical to conduct experiments on humans and other non-human animals? What safeguards are needed to ensure informed consent, safety, and humane treatment?

  2. Research Justification: Are all research questions worth pursuing? For example, how do we evaluate ethically fraught topics such as eugenics (the discredited practice of trying to improve the human population by controlling who can reproduce based on perceived genetic traits), which has a deeply harmful history tied to forced sterilizations, racism, and pseudoscience.

  3. Representation in Research: Is our understanding of psychology overly shaped by the limited populations that have historically been studied? Much of early psychological research was conducted with participants from Western, educated, industrialized, rich, and democratic (WEIRD) societies limiting how generalizable these findings are to the global population. How do factors such as culture, race, ethnicity, gender, etc. impact the extent to which these findings apply to diverse populations?

  4. Application to Society: What are the practical limitations and responsibilities of applying psychological findings to social policy, law, education, and healthcare? For example, many findings from social psychology can be used to influence behavior. But is it ethical to apply these insights to manipulate people?

Ethical questions like these cannot—and should not—be answered by psychologists alone. Drawing on lessons from other fields, it’s essential that administrators, policymakers, and the communities most impacted by psychological research have a voice in these important conversations about ethics and responsible practice. In other words, you don’t need to be a psychologist to contribute to the conversation about what psychologists should study. You should listen to psychologists, and psychologists should listen to you.

One important entity in these conversations is the Institutional Review Board (IRB). At Colorado State University, we have our own IRB, which oversees all human subjects research conducted on campus. The IRB is responsible for reviewing and approving (or denying) research protocols to ensure that studies are conducted ethically and that participants’ rights and well-being are protected.

5 Summary

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Lecture summary.