We do not yet know the precise combination of factors that merge in some fashion to yield a disordered personality. We do know that both nature and nurture play an interactive role.
Several theories have been proposed that attempt to synthesize the available research findings into a more cohesive explanation of how personality disorders may develop. These theories have a very practical application: By describing the various factors that combine to produce personality disorders, these theories simultaneously yield solutions and treatments for personality disorders. Each theory differs in terms of the weight or importance it assigns to these biological, psychological, or social factors. Nonetheless, they each acknowledge there is an important inter-relationship between nature (biology and temperament) and nurture (the social environment and life experiences) in the formation of personality. As such, all of these theories can be described as exemplars of the more generalized biopsychosocial model (BPSM) of human behavior. The BPSM is an integrative model that is widely accepted within the mental health professions. We now turn our attention to the psychosocial component of this model as we explore theories of personality disorders. Following that, we will briefly review the biological component of the model.
Why are there so many theories to explain personality disorders?
Psychologists use theories as a tool for understanding, studying, and predicting human behavior. Thus, psychological theories are one tool we can use to explain how personality development may deviate off the path of healthy development and instead steer toward unhealthy development, or personality disorder. However, as you read through the various theories described below, you may find yourself wondering, "Why are there so many theories? Wouldn't just one theory suffice?" In order to respond to this legitimate concern, it might be useful to draw an analogy between the mind and a house. In order to build a house, an architect constructs a set of plans. Of course, there are many different architectural styles, from modern to traditional. Nonetheless, each architectural plan is still a design for the essential framework of a house. The same is true of theories of personality. There are many different "styles" or ways to describe the mind's architecture, but the end result is the same: each of these different theories describe the framework of the mind, according to different "styles" (different branches of psychology or different schools of thought). Therefore, each design, regardless of its particular "style," is still describing the essential framework of the mind.
Continuing with this analogy between the mind and a house, we might purchase a home but the original architectural plans may be unavailable to us (as is most certainly the case with the human mind!). Thus, when something goes wrong with the house, say for example, an inexplicable leak that develops below the flooring, it is not necessary to view the architectural plans of the house in order to repair the leak. In fact, different people will approach this repair differently. The goal remains the same: to repair the damage. It's the same with the human mind. We do not need to be able to "see" the mind's architecture in order to correct a structural problem. Likewise, different clinicians will use different approaches, but the goal is to repair what was damaged. Thus, the various theories that we discuss below might be said to represent different architectural styles for constructing the framework of the mind. Later, when we discuss the various treatments for personality disorders, these theories are applied to guide the repair of the damaged personality.
A discussion of the theories of personality disorders can become quite difficult and confusing. This is because we must necessarily dive into highly abstract concepts about the architecture of the human mind, and the structures which form the framework of that architecture. Despite these difficulties, we feel this discussion is worthwhile because these theories form the foundation for various treatments. Thus, it may be helpful to understand these theories in order to fully appreciate why these treatments work. However, while this understanding may be beneficial, it is not necessary to fully understand these theories and the reader may wish to skip ahead to the treatment section.