4 Famous Psychologists And Their Theories

Discover 4 of the most famous psychologists of all-time, including their ground-breaking theories which shaped the field of psychology into what it is today.

Katie Broadbent - 13 July 2021 · 16 min read

By its very nature, Psychology, as a field of study, seeks to understand the inner workings of human beings - those extremely complex and distinctive neural networks that shape our every thought, behaviour and personality.

Throughout history, many psychologists have experimented with and presented various theories to understand the unknown, with some leading to major breakthroughs and contributions to our knowledge of Psychology.

In this article, we’ve presented a sample of 4 famous psychologists who have had major influence in the world of psychology. Each of them contributed hugely to our understanding of the human brain and its behaviours, shaping the subject we know it as today.

4 Famous Psychologists and Their Theories

The list below captures just four of the very most famous psychologists and their theories which have shaped their place in history.

While each theorist may not be recognised for having contributed to an overriding school of thought, and while many of their theories may come with a few question marks over their validity, each brought a unique perspective to the field of psychology and made a positive contribution to its discussion. 

Ivan Pavlov (1849 - 1936)

One of the earliest but still very famous psychologists on our list is Ivan Petrovich Pavlov. Although officially trained as a Russian physiologist, he is recognised today as a prominent psychologist of his time, as a result of his work in discovering classical conditioning. 

His work had a major impact on the school of thought of behaviourism, developing the idea that we can be conditioned to respond to things by pure association. 

Today, his classic dog experiment - which, if you study A-Level Psychology, is probably quite familiar to you - remains one of the most famous, with his work in this field so highly respected that he was awarded the Nobel Prize for Physiology or Medicine in 1904. 

Ivan Pavlov’s Classical Conditioning Theory

During the 1890s, Pavlov (by accident) emerged with his theory of classical conditioning after conducting a physiological experiment on dogs. 

His work began by researching the salivation response in these dogs when being fed, where he predicted that dogs would salivate when having food placed in front of them. However, he discovered that dogs would start salivating whenever they heard the footsteps of his assistant in the corridor who was bringing them the food.

Captivated by their physiological behaviours, Pavlov began experimenting, looking to see if other events or objects could trigger the same response when associated with food. Guess what - they did! And so, the idea of classical conditioning was born.

In essence, Pavlov’s theory on classical conditioning identifies how a learning process occurs through associations between an environmental stimulus and a naturally occurring stimulus. It’s all about forming associations between two separate stimuli, resulting in a learned response or behaviour.

Early ideas in behaviourism were based on the assumption that all learning happens through interacting with the environment, with the environment itself shaping our behaviour. But the act of classical conditioning takes this idea one step further. It involves placing a neutral stimulus just before a naturally occurring reflex in order to associate an environmental factor with a learned response. 

For example, in Pavlov’s famous experiment with dogs, he played a metronome sound while dogs salivated in response to food. By associating this neutral stimulus (the sound) with the environmental stimulus (the food), he found that over time, the sound of the tone alone could produce the salivation response. 

Pavlov’s experiment showed that it was possible to form an association between two stimuli, resulting in a learned response. But he also learned that there are three separate stages of this process:

Phase 1: Before

The first stage of the classical conditioning process requires a naturally occurring stimulus that will automatically elicit a physiological response. 

During this stage, the unconditioned stimulus (e.g. the food) automatically triggers a response in an animal or human (e.g. salvation). There is also a neutral stimulus (the sound) that produces no response as of yet - not until it has been paired with the unconditioned stimulus.

Phase 2: During

In the second phase of the classical conditioning process, the previously ‘neutral stimulus’ (the sound) is repeatedly paired with the unconditioned stimulus (the food). As a result, an association between them both is formed.

At this point, the neutral stimulus now becomes known as a conditioned stimulus, as the participant has now been conditioned to respond to that stimulus. Now it has been associated with the unconditioned stimulus, it will evoke a conditioned response. 

Phase 3: After

Now that the unconditioned stimulus and conditioned stimulus have formed an association, whenever the conditioned stimulus is presented, a physiological response will occur even without an unconditioned stimulus. 

This resulting response is known as the conditioned response and refers to the learned response to the previously neutral stimulus. For example, in Pavlov’s experiment, the conditioned response would be the dogs salivating automatically when hearing the sound of the metronome. 

Over the years, Pavlov’s experiments have been criticised for their applicability to the real world. In reality, people do not evoke the same responses as dogs, and so the idea of classical conditioning can only be used to explain certain behaviours. 

With that being said, his theory has helped in the development of certain psychological treatments for those who suffer with generalised mental health illnesses. For example, many CBT therapists pair anxiety-provoking scenarios with relaxation techniques in order to create an association between them - ultimately, with the aim of reducing anxious feelings towards the environment or behaviour which evokes that particular response. 

Sigmund Freud (1856 - 1939) 

Photo credit: ThoughtCo

Quite possibly one of the most famous clinical psychologists in history, Sigmund Freud was a leading contributor to the development of psychology, having developed ground-breaking theories about the nature and workings of the human mind. 

Most notably, he is recognised as the founding father of ‘psychoanalysis’ - a theory which both explains human behaviour and is also used as a methodology for treating mental illness. 

Much of his work was dominated by a desire to seek an understanding of the things we don’t say or often camouflage from other people. That is, our unconscious mind - its structure and obscurities, including how it cultivates our personalities from childhood to adulthood. 

As such a great influence in Psychology, much of Freud’s lexicon has become embedded within the vocabulary of Western society. Words he introduced through his theories are now part of our common dialogue, including; repression, cathartic, and neurotic, to name a few. 

Freud’s Psychoanalysis Theory

Although he had many, Freud’s theory on Psychoanalysis is possibly one of his most famous. 

The theory was based on the idea that events in our childhood have a great influence on our adult lives, shaping our personality and affecting our mental health. For example, if someone suffered from a traumatic experience in their childhood but blocked it out of their consciousness, this could lead to problems in the future (called neuroses). 

The ground-breaking case that led to the development of this theory is recognised as ‘The Case of Anna O.’ Anna (not her real name) came to Freud’s teacher (Josef Breuer) while suffering from hysteria - a condition which affects the patient physically, with symptoms including hallucinations, paralysis, and loss of speech, without having developed from a physical condition.

Freud saw Anna successfully recover from her hysteria when Breuer treated her by encouraging her to recall forgotten memories of traumatic events. During these conversations, seemingly obvious parallels were drawn between Anna’s fears and her previous experiences. For example, she had a fear of drinking which had developed after a dog she was scared of had drank from her own glass.

Breuer discussed the case with Freud, which he then used as inspiration for all future studies. He later published his book Studies in Hysteria (1895), where he proposed that physical symptoms are often manifestations of deeply repressed traumas. 

Freud’s Unconscious Mind Theory

In the early 20th century, Freud began to develop a topographical model of the human mind, whereby he described the structure and function of different parts of our thinking systems. And this is where his second-most famous theory was born: his theory on the unconscious mind.

Using the analogy of an iceberg to describe the three levels of the mind; on the surface is our consciousness which consists of the thoughts which are the focus of our attention now; then, there is the preconscious which sits below, and consists of all thoughts which can be retrieved from memory.

Finally, the third and most significant region is the unconscious, which Freud claimed to hold all the things which cause most of our behaviour. Just like an iceberg, he claimed the unconscious, deeply rooted and hidden within our minds,  was much bigger than any would anticipate.

The unconscious mind, he proposed, acts as a repository for primitive wishes and impulses which are kept at bay by the preconscious area. And this area, he believed, governs behaviour to a greater degree than people expect, shaping our personalities to develop certain neuroses. Indeed, it is then through the method of psychoanalysis that we can bring these thoughts and behavioural desires to the surface. 

These are just a couple of the main Freudian theories. For further information and reading on Freud’s incredibly fascinating ideas, the Simply Psychology website provides a great overview.

Jean Piaget (1896 - 1980)

Photo credit: Flexible Learning Strategies

Third on our list of famous psychologists is Jean Piaget, a Swiss psychologist known for his intuitive work on child development and placing importance on the early education of children.

His interest in child development grew from his experience as an assistant to psychologists  Alfred Binet and Theodore Simon during their developmental work to standardise their famous IQ test. During his role here, he was captivated by understanding the different levels of intelligence amongst individuals and how their motor and emotional skills developed at varying rates.

Much of his work centred around observations of his own nephew and daughter. Up until the early 20 century, children were largely treated as smaller versions of adults. But Piaget led the case in proving that the way children think and learn is far different to the way that adults do. 

His observations were so well-received that even world-leading thinkers including Albert Einstein commented on his obvious yet incredibly ground-breaking theory; "so simple only a genius could have thought of it."

Piaget’s Cognitive Development Theory

Jean Piaget is famed for his work on understanding the development of brains amongst children during their earliest years. Mainly, he was occupied with understanding how levels of intelligence vary between students, as well as their ways of acquiring knowledge.

After many years of observation, theory, and experimentation, he concluded that children are not necessarily less intelligent than adults, but they simply think and obtain new information differently to them.  

He discovered that children take an active role in their learning process, conducting their own experiments, asking questions, and observing the world to draw their own understanding on things. The more that children interact with the environment around them, the more they build new understandings on top of their existing knowledge, and adapt previous ideas to accommodate for new information.

His theory of ‘Cognitive Development’ suggests that children move through four stages of mental development. Rather than children all thinking the same and learning at the same rate, he proposed that there are both qualitative and quantitative differences between age groups. These four stages are as follows:

Sensorimotor stage (0-2 years):

The sensorimotor stage is a period of immense growth and learning. As infants begin to interact with their environment, they continually make new discoveries about how the world works.

Major characteristics and developmental changes include:

  • Infant learns through movements and sensations: grasping, looking, and listening

  • Object permanence - Infants learn that things exist even when they cannot be seen

  • Learn that their actions can cause things to happen in the world around them

Preoperational stage (2-7 years):

At this stage of their development, children learn through play, but often struggle with logic and understanding other peoples’ perspectives.  They become much more skilled at pretend play during this stage of development, but still think about the world around them very concretely. 

Major characteristics and developmental changes include:

  • Children think symbolically - learning to use words and pictures to represent objects

  • They are egocentric and struggle to understand others’ perspectives

  • Although their language is more developed, children continue to think about things in very concrete terms

Concrete operational stage (7-11 years):

While at this age children are still very literal in their thinking, they begin to be much more adept at using logic. As such, their egocentrism begins to fade as children use their new-found skill at becoming better at thinking about how other people may view a situation. 

Major characteristics and developmental changes include:

  • Children begin to think logically about concrete events

  • Thinking becomes more logical and organised, but still very concrete

  • Children begin applying inductive reasoning to a general principle

Formal operational stage (12+ years):

The final stage of Piaget’s Cognitive Development theory involves a rise in logical thinking, along with the introduction of being able to consider abstract concepts. At this point, individuals become much more capable of being able to consider multiple possibilities at once, and think more scientifically about their world. 

Major characteristics and developmental changes include:

  • The adolescent/young adult begins to think abstractly

  • They can begin to think more about philosophical, moral, and social issues that require more theoretical and sometimes hypothetical reasoning

  • Begin to use deductive logic from a general principle to specific information

One important point to note about Piaget’s theory is that he did not view children’s intellectual development as a quantitative process; that is, they don’t just keep adding it to a bank of existing information. Instead, he proposed that there is a qualitative change, with children changing the way they think and process information during the four stages of development.

Albert Bandura (1925 - )

Photo credit: Positive Psychology

The late 1960s were a period of great development for cognitive psychology. Canadian psychologist, Albert Bandura, and his social learning theory were part of this great revolution, emphasising the complexities of learning and behaviour in social settings.

His, along with many other social psychologist's ideas were a shift beyond classic behavioural theories, which suggested that all behaviour is a result of conditioning (Pavlov), reinforcement and punishment. Instead, they proposed that all learning was instead a result of direct experience with the world around them, through the process of simply observing the actions of others. 

As the old analogy goes, children are very much “like sponges,'' soaking up all the different interactions and experiences they have each day. And it was much of Albert Bandura’s work that proposed how observational learning and modelling play a critical role in how a child shapes their own behaviour and decision making. 

Albert Bandura’s Social Learning Theory

Simply put, Bandura’s social learning theory proposes the idea that social behaviours can be acquired through observation and imitation of others. This is because quite often, children and adults can exhibit certain actions or behaviours even when they’ve had no direct experience. 

For example, if you’ve never ridden a bicycle before, you would probably know what to do if someone passed you a bicycle and asked you to try and ride it. This is because you’ve probably seen others perform this action before, either in-person or on television/in film. 

This theory went beyond traditional ‘conditioning’ influences, instead suggesting that pure observation is enough for someone to copy a behaviour. Known as observational learning, this type of learning can be used to explain how a variety of behaviours can occur in people who have never been encouraged or conditioned to do them before.

Central to the social learning theory are three core concepts, which are as follows:

1. People can learn through observation

During the development of his theory, Bandura conducted the world-famous ‘Bobo experiment’ to explain how children learn behaviours they have observed from others. 

In the study, children watched an adult act violently toward a Bobo doll. When the children were then allowed to play in a room with the Bobo doll, they began to imitate the aggressive behaviours they had previously observed. 

From these experiments, Bandura then identified three scenarios and models  where observational learning can take place:

  • A live model - where an actual individual demonstrates a behaviour

  • A symbolic model - where real or fictional characters display behaviours (in films, books, TV, etc.)

  • A verbal instruction model - involving descriptions and explanations of behaviour

2. Our internal mental states impact our learning

Bandura argued that an essential component of observational learning is determined by our mental states, and cannot be explained by external, contextual reinforcement. That is, our own motivations play a role in deciding whether to copy a behaviour or not. 

He used the term ‘intrinsic reinforcement’ as a way to describe internal regards, such as a sense of achievement. And it's these internal forces, and our own judgements on morality which determine whether we choose to imitate a behaviour.

3. Just because something has been learned, it doesn’t mean it will always result in a change in behaviour

When you teach someone to swim, you can quickly determine if they’ve learned the skill by being able to swim a short distance, unassisted. Likewise, when you teach someone how to knit, you can watch them perform the action independently to see if they’ve understood all instructions. 

But quite often, we can learn certain behaviours without it becoming obvious to others. For example, we may learn how to change a tyre by watching a demonstration video, but we may never choose to use that behaviour if we have someone in the car that can also change a tyre.

The final concept in Bandura’s social learning theory identifies that even though learning may have taken place, it doesn’t mean it will lead to a permanent change in behaviour. In fact, we can observationally learn something without then demonstrating it, ever.


Throughout history, psychologists (and some physiologists too!) have made incredibly fascinating and equally important contributions to our understanding of the human mind and behaviour. 

And while over time, some of their theories and ideologies have been adapted and added to thanks to an increased development of research, they are still recognised as some of the most ground-breaking theorists of the early to mid-twentieth century. 

This list represents just a very , very small sample of the most famous psychologists and their theories that have mapped out much debate in psychology. But there are so many more interesting psychologists and theorists out there who have inspired much of the field of psychology. 

Keep researching, and get inspired.

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