In the 19th and early 20th centuries, there was a school of psychology known as structuralism, represented by such figures as Wilhelm Wundt and Edward B. Titchener. The structuralists used introspection to attempt to describe the elementary components of the human mind. For example, according to the structuralists, a sensory perception was based on the structure of the associations between numerous sensations (whence the name “structuralism”). The structuralists believed that by describing the possible

combinations of these elements, they could deduce laws as general and powerful as those governing the physical world. The structuralist approach was criticized not only because of its implicit dualism, but also because of the difficulty of experimentally testing the introspection on which it was based. In response, another school of thought emerged that was radically

opposed to structuralism. This school was known as behaviourism. According to its pioneers, such as John B. Watson and B. F. Skinner, no scientific approach to psychology could be built on subjective states, which are essentially private. In contrast, their new psychology would be based not on personal judgments about feelings and states of mind, but solely on the experimental study of behaviour. To make psychology a true science, the behaviourists decided to study

only observable phenomena: the stimuli to which an organism is subjected, and the responses that it makes to these stimuli. The behaviourists thus treated the brain as a “black box”, in the sense that they regarded what happened inside it as being unobservable by its very nature