The social penetration theory (SPT) proposes that as relationships develop, interpersonal communication moves from relatively shallow, non-intimate levels to deeper, more intimate ones. The theory was formulated by psychologists Irwin Altman of the University of Utah and Dalmas Taylor of the University of Delaware in 1973 to understand relationship development between individuals. Altman and Taylor noted that relationships "involve different levels of intimacy of exchange or degree of social penetration". SPT is known as an objective theory as opposed to an interpretive theory, meaning it is based on data drawn from actual experiments and not simply from conclusions based on individuals' specific experiences. SPT states that the relationship development occurs primarily through self-disclosure—when one intentionally reveals information such as personal motives, desires, feelings, thoughts, and experiences to others. This theory assumes that as people becomes closer with others, positive reinforcement through positive interactions allow people to achieve deeper levels of intimacy. The theory is also guided by the assumptions that relationship development is systematic and predictable. SPT also examines the process of de-penetration, how some relationships regress over time, and eventually end. Assumptions SPT is based on four basic assumptions: Relationship development moves from superficial layers to intimate ones. For instance, people tend to present their outer images only, talking about hobbies on a first date. As the relational development progresses, wider and more controversial topics such as political views are included in the dialogues. Interpersonal relationships develop in a generally systematic and predictable manner. This assumption indicates the predictability of relationship development. Although it is impossible to foresee the exact and precise path of relational development, there is a certain trajectory to follow. As Altman and Taylor note, "[p]eople seem to possess very sensitive tuning mechanisms which enable them to program carefully their interpersonal relationships." Relational development can move backward, resulting in de-penetration and dissolution. For example, after prolonged and fierce fights, a couple who originally planned to get married may decide to break up and ultimately become strangers. Self-disclosure is the key to facilitate relationship development, and involves disclosing and sharing personal information to others. It enables individuals to know each other and plays a crucial role in determining how far a relationship can go, as gradual exploration of mutual selves is essential in the process of social penetration. Self-disclosure Self-disclosure is a purposeful disclosure of personal information to another person. Disclosure may include sharing both high-risk and