In 1938, Henry Murray developed a system of needs as part of his theory of personality, which he named personology. He argued that everyone had a set of universal basic needs, with individual differences on these needs leading to the uniqueness of personality through varying dispositional tendencies for each need; in other words, a specific need is more important to some than to others. In his theory, Murray argues that needs and presses (another component of the theory) acted together to create an internal state of disequilibrium; the individual is then driven to engage in some sort of behavior to reduce the tension. Murray believed that the study of personality should look at the entire person over the course of their lifespan – that people needed to be analysed in terms of complex interactions and whole systems rather than individual parts – and an individual's behaviors, needs and their levels, etc. are all part of that understanding. Murray also argued that there was a biological (specifically neurological) basis for personality and behavior.^[1][2]

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 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 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.^[1] Frustration of these psychogenic needs plays a central role in the origin of psychological pain.^[3] 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.^[2] 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.

Murray argued environmental factors play a role in how psychogenic needs are displayed in behavior. He used the term "presses" to describe external influences on motivation that may influence an individual's level of a need as well as their subsequent behavior.^[1][2] The "press" of an object is what it can do for or to the subject.

Any stimulus with the potential to affect the individual in a positive or negative way is referred to as "pressive", and everything else is referred to as inert. "Pressive Perception" is how the subject interprets a press as either a positive or negative stimulus. "Pressive Apperception" refers to the subjects anticipation that the stimulus will be perceived as either positive or negative. Murray notes that both Pressive Perception and Apperception are largely unconscious. Presses may have positive or negative effects, may be mobile (affecting the subject if they do nothing) or immobile (affecting the subject if they take an action), and may be an alpha press (real effects) or a beta press (merely perceived).

Murray divides needs into several binary categories: manifest (overt) or latent (covert), conscious or unconscious, and primary (viscerogenic) and secondary (psychogenic) needs.^[1] Manifest needs are those that are allowed to be directly expressed, while latent needs are not outwardly acted on.^[4] Conscious needs as those that a subject can self-report, while unconscious needs are all others. This is distinct from manifest versus latent in that a person may directly express a need they are unaware of, or not express a need they are aware of. The categorization most commonly referred to is the division between primary (viscerogenic) and secondary (psychogenic) needs.

Although Murray's theory has had a substantial influence on personality testing and research, some critics say that his system of needs is too broad and rather subjective. One criticism of this hierarchy is that it lacks the objective criterion for needs.^[8] It can also be said that some of the needs can conflict with each other like achievement and nurturance, which deal with opposing ideas of having to obstacles with achievement being active and nurturance being passive.^[1] This could possibly be due to contrasting instructions from the experimenters.^[2]

• Maslow's hierarchy of needs