The scope of psychology, then, is as broad and varied as human existence itself. In order to make the discipline manageable, psychologists have sub-divided it into a number of specialized fields. For example, developmental psychologists study how human beings change as they age. Cognitive psychologists study thinking processes, including memory and information processing. Others focus on principles of learning or motivation.
Social psychologists study our thinking and behaviour as influenced by others.
In spite of this diversity, most psychologists share a number of fundamental assumptions in common. Foremost among these is the belief these phenomena actually can be studied in the first place. Central to this is the belief that principles of scientific inquiry can be applied to research on human beings. For example, most psychologists believe that much of what people think and do can be quantified and studied statistically. Many psychologists today believe this to be true even for behaviour that is not readily observable, such as our thought processes and our sensory and perceptual mechanisms.