Psychology is a science still in its infancy, but that doesn’t mean people are only interested in human behaviour in recent centuries. Classical Chinese philosophers like Laozi, Confucius, and Mencius have been interested in matters of the mind as early as the 5th Century BCE. Laozi observed that having a ‘right mind’ will lead to our lives to falling in place. He also pioneered the idea of ‘wuwei’ (read more at: https://thepsychologist.bps.org.uk/volume-28/november-2015/wu-wei-doing-less-and-wanting-more), which suggests that we should be less deliberate in the ways we lead our lives, which latter corroborates with Buddhism’s core tenet that ‘desire is suffering’ (in modern psychology, dissatisfaction is often aroused when there is a mismatch between expectations and actual feedback). Indeed, our early human ancestors have been extremely interested in developing practical wisdom of the mind and much of these wisdom holds true by modern standards.
However, most of the psychology we know was developed mainly in the west, mainly led by Plato and Socrates. Plato suggested that our mind lies in our brain (it wasn’t common sense back then!), while Socrates proposed that it might lie in our heart (to be more precise, it is the vagus nerve that plays the a part in our decisions). Plato was one of the earliest thinkers to think that the soul had several components: reason, spirit, and appetite (which almost certainly became an inspiration for Freud’s psychoanalytic theory). Plato also studied human pleasures and their ranked orders, along with morality. His disciple, the great Socrates, invented what is known as the Socratic method of enquiry. While this started off as way of debate and primitive science, it later on formed the core tenets of cognitive therapy. It is as if people are already doing positive psychology before the common era even began.
Except, these ideas were not scientifically tested yet. The scientific method had yet to exist.
The study of minds remained in the domain of philosophy for an extended period in human history, but it was in the early 17th century where the field had many well documented developments, with debates that still haven’t seen resolution today. It was a great period for both philosophies of mind and science. David Hume and John Locke contributed greatly to the empirical, experience-based, philosophy of science. Famed philosopher Rene Descartes suggested that the mind is a separate entity from the body, which might have influenced the separation of psychiatry (mind medicine) from neurology (brain medicine). It was also a period for the rise of many political philosophers such as Thomas Hobbes, Karl Marx, and Jeremy Bentham, where their interest in politics also led them to discuss a lot about human behaviour and nature. All of these combined with the rise of existentialism (which is still a strong influence in modern psychotherapy and personality theory) led by Nietzsche and Heidegger. This era has been full of thinkers vital to the development in our collective understanding of both science and mind.
This science-mind integration first saw the birth of psychiatry. The mentally ill were not treated humanely as their illnesses stripped them of their humanity in the eyes of the public. It was also around this era that Philippe Pinel released many of these patients from their wards, which will have a lasting impact for a more humanistic approach towards psychopathology.
Neurology also experienced considerable development at this time. The early 1800s saw the birth of phrenology (nowadays largely scrutinized as a pseudoscience) by Franz Gall, who believed that the shapes of our skull can reveal patterns in our personality. Following this were studies on language brain interaction (speech production and speech comprehension are different pathways localized in the brain) by Paul Broca and Carl Wernicke. It is no coincidence that the emerging field of psychology will be close contemporaries with neuroscience, and many psychologists would too pursue a career in neuroscience.
Psychology formulated much later, just short of half a century later after the publication of Origins of Species by Charles Darwin. It is difficult to track who actually came first, but both William James and Wilhelm Wundt were the forefathers of psychology and started the first ever experimental psychology labs in their own countries (The US and Germany respectively). Wilhelm Wundt’s school of thought would employ introspection and break down these experiences into smaller components, while William James would adopt a more evolutionary perspective to understand how our mental functions help us. Both schools of thought are no longer used, but both would have lasting impact on how psychology works.
Psychology would continue to develop, with different waves of perspectives emerging from different countries. Sigmund Freud will first rise as a prominent neurologist before developing psychoanalytic theory, which will inspire many others to readapt their own version of psychodynamics to better model how our unconscious works (and unfortunately, skewing the perception of psychology due to its lasting influence in pop culture).
This will eventually be took over by behaviourism, unintentionally pioneered by Ivan Pavlov and popularized by John Watson and Burrhus Skinner. This paradigm had been radical in the sense that it dismisses all forms of internal psychological works, and prefers to reduce all psychology to observable behaviour. Now again, behaviourism is no longer fashionable but its core tenets, archaic as it seems, are still capable of providing very powerful explanations in the psychology of learning.
These waves of psychology had been lacking one crucial component, which is the whole person. Psychoanalysis diminished the holistic idea of humanity by reducing humans to their unconscious, while behaviourism monolithically dismissed the need to understand the human experiences by focusing only on outward behaviors. These brands of psychology could not satisfy the desire to want to know humans better, thus coupled with the human potential movement, humanistic psychology happened. This wave is spearheaded by quite possibly the most influential psychotherapist in history, Carl Rogers. Carl Rogers believed that humans are more than the products of conditioning and their unconscious impulses, as they are capable of choosing and doubting while striving to be better. Rogers recognized that every single being has potential and is a work in progress, which a monolithic view of science will fail to notice. Psychology began to look at whole-person ideas such as motivations, while the fields of counseling and psychotherapy took a modern, non-judgmental turn.
Around the mid 20th century, an intellectual movement turned people to recognize the importance of information processing and decision, which the major waves of psychology have largely ignored. This is known as the cognitive revolution, which psychology started to use methods from computer science and artificial intelligence. American psychology start to push away radical behaviourism and start to adopt more computational models of human decisions in their research, while bringing in European psychologists who have already made some progress in cognitive psychology. Psychology mainly turned to language, memory, perception, and problem solving, which is still a mainstay in modern psychological research.
This brings us to our modern times. The mot influential area now is positive psychology, a more scientific remaster of humanistic psychology, which is now seeping into the applied areas of developmental psychology and organizational psychology. There are also resurrections of ancient wisdoms, most notably mindfulness meditation, which shows to have benefits that can survive rigourous neuroscientific testing. Overall however, psychologists no longer have rigid schools of thought (Read here for psychologists from various specializaitons https://thebestschools.org/features/most-influential-psychologists-world/). People aspiring to work with psychology will not have to subscribe to monolithic philosophy aside from aspiring to produce good science rather than trying to market ideas for personal profit.