Murray defines a need as a drive that has the potential to prompt a behavior from the person. For example, the need for affiliation may drive a person to join a social organization. Needs are often influenced by environmental stimulus or "presses", another component of Murray's theory. Individual differences in levels of needs lead to the uniqueness of a person's personality; in other words, specific needs may be more important to some people than to others. According to Murray, human needs are psychogenic in origin, function on an unconscious level, and can play a major role in defining personality. He also believed that these needs could be measured by projective tests, specifically one he had developed, known as the
thematic apperception test (TAT). Unlike
Maslow's hierarchy of needs, Murray's needs are not based on a hierarchy; individuals may be high in one and low in the other, and multiple needs may be affected by a single action. Murray differentiated each need as unique, but recognized commonalities among them, codified at least partially in his categorization system. Behaviors may meet more than one need: for instance, performing a difficult task for your fraternity may meet the needs of both achievement and affiliation. While each need is important in and of itself, he also believed that needs can support or conflict with one another, and can be interrelated. He coined the term "subsidation of needs" to describe when two or more needs are combined in order to satisfy a more powerful need, and the term "fusion of needs" to describe when a single action satisfies more than one need. For example, the need for dominance may conflict the need with affiliation when overly controlling behavior drives away family, romantic partners, and friends. A need may be a purely internal state, but more often it is evoked by a press. == Presses ==