Psychopath and sociopath are often used interchangeably in common speech to describe a person who is pathologically prone to criminal or violent behavior and who lacks any regard for the feelings or interests of others and any feelings of remorse or guilt for his crimes. Although the terms are also used in the scientific literature (including the Diagnostic and Statistical Manual of Mental Disorders, or DSM), they are not well defined there; mental health professionals instead prefer to understand both psychopathy and sociopathy as types of antisocial personality disorders (APDs), each condition being distinguished by a few characteristic features but both having many features in common.

Both psychopathy and sociopathy, then, are characterized by an abiding pattern of disregard for and violation of the rights of others, as manifested through three or more of the following habitual or continual behaviors: (1) serious violations of criminal laws; (2) deceitfulness for personal gain or pleasure, including lying, swindling, or trickery; (3) impulsiveness or failure to plan ahead; (4) irritability and aggressiveness often resulting in physical assaults; (5) reckless disregard for the safety of oneself or others; (6) failure to meet important adult responsibilities, including job- and family-related duties and financial obligations; and (7) lack of meaningful remorse or guilt—to the point of complete indifference—regarding the serious harm or distress one’s actions cause other people.

Other characteristics associated with APD are a pronounced lack of empathy; a tendency to be contemptuous of the rights, interests, or feelings of others; and an excessively high self-appraisal—i.e., arrogance, conceitedness, or cockiness.

Psychologists and psychiatrists emphasize that APD cannot be properly diagnosed in children, because it is by definition a condition that abides for many years and because the personalities of children are constantly evolving. Nevertheless, adults who develop APD typically displayed what is called conduct disorder as children, generally characterized by aggressive behavior toward people or animals, destruction of property, deceitfulness or theft, and serious infractions of criminal laws or other norms.

Among persons who display APD, those called psychopaths are distinguished by a nearly complete inability to form genuine emotional attachments to others; a compensating tendency to form artificial and shallow relationships, which the psychopath cynically exploits or manipulates to benefit himself; a corresponding ability to appear glib and even charming to others; an ability in some psychopaths to maintain the appearance of a normal work and family life; and a tendency to carefully plan criminal activities to avoid detection. Sociopaths, in contrast, are generally capable of developing a close attachment to one or a few individuals or groups, though they too generally have severe difficulties in forming relationships. Sociopaths are also usually incapable of anything even remotely resembling a normal work or family life, and, in comparison to psychopaths, they are exceptionally impulsive and erratic and more prone to rage or violent outbursts. Accordingly, their criminal activities tend to be spur-of-the-moment rather than carefully premeditated.

Although both biological and environmental factors play a role in the development of psychopathy and sociopathy, it is generally agreed that psychopathy is chiefly a genetic or inherited condition, notably related to the underdevelopment of parts of the brain responsible for emotional regulation and impulse control. The most-important causes of sociopathy, in contrast, lie in physical or emotional abuse or severe trauma experienced during childhood. To put the matter simplistically, psychopaths are born, and sociopaths are made.

Both psychopathy and sociopathy, and APD generally, share features with narcissistic personality disorder (NPD), the condition exhibited by persons commonly called narcissists. Like persons with APD, narcissists generally lack empathy and tend to have unrealistically high opinions of themselves, and, like psychopaths, narcissists tend to form shallow relationships, to exploit and manipulate others, and to be glib and superficially charming. Unlike many persons with APD, however, narcissists are generally not impulsive, aggressive, or habitually deceitful. Nor do they characteristically display conduct disorder during childhood or criminal behavior in adulthood. Narcissists also characteristically manifest a compelling need for the admiration, esteem, or envy of others, a trait not displayed by persons with APD.