Psychology’s subject of study is people, which makes for one of the unique challenges of psychology as a science: having a basic understanding of people is a prerequisite for functioning in a society made up of other people. As a result, most people have the impression they understand people to some degree. Combined with humans’ ability to see patterns, this means it’s easy for a given explanation of human psychology to seem realistic.
This makes the systematic nature of the scientific method particularly valuable in psychology. Perhaps that is why the starting point of psychology as a science is often placed at 1879, when Wilhelm Wundt founded the first laboratory for studying the mind experimentally. Taking this as a starting point makes sense given that the experimental procedure is at the core of the scientific method. However, since people have been thinking about people for thousands of years, so one could also argue that psychological science is much older.
A second challenge facing the researcher of psychology is that there is no way to directly observe the subject under study (the human mind). After the statement that clearly, ‘something exists’, matters quickly become messy. Besides the brain, psychology does not deal with so-called ‘natural kinds’. Explaining the mechanics of the human mind, however, does require distinguishing something akin to moving parts that together form those mechanics.
Direct observation being impossible, one can claim anything as to potential elements of the human mind and how they interact. Verifying such claims would first require observation of some kind; some way to measure the mind’s content. This can be realised by defining for those elements how they can be measured, which is therefore often specified in the psychological theories that describe postulated explanations.