Voluntarism stems from the concept of voluntary action, in which a person consciously perceives or does something. Voluntarists believed that people perceive things through perception and apperception. Perception is the means by which a person passively takes in a certain observation, such as seeing a dog. Apperception refers to the way in which a person actively takes in a certain observation and interprets it in conjunction with memory of past experiences, such as seeing a dog and recalling emotions of fear as a result of a traumatic experience with dogs.
Structuralism takes the main tenets of voluntarism, namely perception and apperception, and breaks consciousness down into small physical and chemical components. Structuralism uses a technique called "introspection" to break down a person's perception into the most basic units. For example, an individual says that she saw a Broadway show, but, through introspection, she might instead claim to have seen multiple people on a stage dancing and singing with a variety of costumes. The breaking down of both physical and mental phenomena is the fundamental idea of structuralism.
Because structuralism is a school of thought within the voluntarism ideology, they share many characteristics, but the primary difference is that structuralism aims to study the elements of experience, whereas voluntarism looks at perception as a whole. Voluntarism studies the ways in which a person perceives and interprets things within overall consciousness. Structuralism seeks to study the individual parts of consciousness. For example, voluntarism might deal with how a person passively hears sounds that influence his mental state. A structuralist might take these findings and analyze the eardrum and brain to determine why they produce this mental state.
Today, psychologists no longer study voluntarism or structuralism, except in a historical way. However, Wundt's and Titchener's works represent some of the foundational explorations of the subconscious and conscious experience, which influenced early American and German psychology. In addition, many refer to Wilhelm Wundt as the "father of psychology" because of his contributions to the discipline and the school of psychology that he oversaw.