Psychology is really a very new science, with most advances happening over the past 150 years or so. However, it's origins can be traced back to ancient Greece, 400 – 500 years BC. The emphasis was a philosophical one, with great thinkers such as Socrates influencing Plato, who in turn influenced Aristotle.
Philosophers used to discuss many topics now studied by modern psychology, such as memory, free will, attraction etc.
In the early days of psychology there were two dominant theoretical perspectives. An American psychologist named William James (1842-1910) developed an approach which came to be known as functionalism. He argued that the mind is constantly changing and it is pointless to look for the building blocks of experience. Instead, focus should be on how and why an organism does something. It was suggested that psychologists should look for the underlying cause of behavior and the mental the processes involved. This emphasis on the causes and consequences of behavior has influenced contemporary psychology.
Structuralism was the name given to the approach pioneered by Wilhelm Wundt. The term originated from Edward Titchener, an American psychologist who had been trained by Wundt. Structuralism relied on trained introspection, a research method whereby subjects related what was going on in their minds while performing a certain task. However, it proved to be unreliable method because there was too much individual variation in the experiences and reports of research subjects.
Despite the failing of introspection Wundt is an important figure in the history of psychology as he opened the first laboratory dedicated to psychology in 1879, and its opening is usually thought of as the beginning of modern psychology. Wundt was important because he separated psychology from philosophy by analyzing the workings of the mind using more objective and standardized procedures.
Because psychology is a science it attempts to investigate the causes of behavior using systematic and objective procedures for observation, measurement and analysis, backed-up by theoretical interpretations, generalizations, explanations and predictions.
The classic contemporary perspectives in psychology to adopt these strategies were thebehaviorists, who were renowned for their reliance on controlled laboratory experiment and rejection of any unseen or subconscious forces as causes of behavior. And later, cognitive psychology adopted this rigorous, scientific, lab based scientific approach too.
With its broad scope, psychology investigates an enormous range of phenomena: learning and memory, sensation and perception, motivation and emotion, thinking and language, personality and social behavior, intelligence, child development, mental illness, and much more.
Furthermore, psychologists examine these topics from a variety of complementarypsychological perspectives.
Each psychological perspective is underpinned by a shared set of assumptions of what people are like, what is important to study and how to study it. Some conduct detailed biological studies of the brain, others explore how we process information; others analyze the role of evolution, and still others study the influence of culture and society.
Kuhn (1962) argues that a field of study can only legitimately be regarded as a science if most of its followers subscribe to a common perspective or paradigm. Kuhn believes that psychology is still pre-paradigmatic, while others believe it’s already experienced scientific revolutions (Wundt’s structuralism being replaced by Watson’s behaviorism, in turn replaced by the information-processing approach). The crucial point here is: can psychology be considered a science if psychologists disagree about what to study and how to study it?