An early school of psychology used introspection to study the basic elements of mental experiences. this school of psychology was called

The answer is structuralism. It is a 20th Century knowledgeable movement and tactic to the human sciences that tries to analyze a specific field as a complex system of correlated parts. Largely speaking, Structuralism grasps that all human activity and its products, even perception and thought itself, are created and not natural, and in specific that everything has meaning because of the language system in which we function. It is closely connected to Semiotics, the study of signs, symbols and communication, and how gist is built and understood.

Complementary goods. they go together, thats why one price increase and the others demand increases