The diagnosis of personality disorder generally implies the idea of intractability and frequently leads to a lack of proper medical care. This attitude is the expression of a negative, moralising, and, according to Tyrer et al.,⁽⁸⁾ delusional attitude of the doctor towards the patient. Cusack and Malaney⁽⁹⁾ posed the question as to whether patients with antisocial personality disorders are ‘bad’ or ‘mad’. They attempted to establish differential criteria in order to show that if patients with an antisocial personality disorder are not ‘mad’, then they must be considered as ‘bad’ and therefore must be delivered to the judicial system, after diagnosis and treatment of secondary symptoms. In 1999, the UK Government 1999 introduced a new concept: Dangerous and Severe Personality Disorder (DSPD). This subsequently became a treatment and assessment program for individuals who satisfy three requirements: 1) have a severe disorder of personality, 2) present a significant risk of causing serious physical or psychological harm from which the victim would find it difficult or impossible to recover, and 3) the risk of offending should be functionally linked to the personality disorder.^{(10, 11)}

Dualism has been present in psychiatry since its origins as specialty. According to Griesinger:⁽¹²⁾

The radical separation between mental-brain illnesses and ‘aberrations of intelligence’ is fundamental to modern psychopathology. Schneider⁽¹³⁾ distinguished between psychoses as pathological conditions of the brain (disease or defective structure) and variations of the psychic way of being. Abnormal personalities, personality disorders, and neurotic disorders belong to the second category.

Schneider⁽¹⁴⁾ defines some abnormal personalities in a statistical sense, to describe those individuals whose form of feeling, experience and behaving differs to a certain degree from what is considered to be normal for most individuals in a social group. Some of these are psychopathic personalities who, as a result of their abnormality, suffer or make others suffer. It should be stressed that according to Schneider’s statistical definition of personality and the dualism of his psychopathological system, the only possible criterion to define a clinical condition in the absence of a brain disease is the suffering, the pathos. Suffering is for Schneider the reason why some people ask for medical care, but not a sufficient criterion for to determine the presence of an illness. Schneider had to add suffering inflicted on others (social suffering) in order to be able to include certain kinds of abnormal personalities characterized by the absence of personal suffering (heartless psychopaths, sociopaths).

It seems acceptable to consider as a patient someone who suffers and asks for clinical care although the criterion for suffering is a weak one when compared with the presence of an illness of an organ. On the contrary, the criterion of induced suffering which characterises some psychopathic personalities, defined following Schneider, is not acceptable in medicine and it is surprising that this has been little criticised. The clue lies in Schneider’s definition of personality which excludes any biological substrate.⁽¹⁵⁾ The effect of viewing psychopathies as simple variations was to reduce the amount of neurobiological research into the neuroses and personality disorders because they were not considered amenable to natural scientific methods. The study of the personality was left the new psychoanalytical and psychological theories.

Nowadays it is impossible to maintain such a reductionistic perspective, and it is recognised that the morbid nature of personality disorders can be understood through the study of changes in its biological substratum. There are not two kinds of mental disorders, the psychosis which are the consequences of brain illnesses, and the variations of the psychological way of being (neurosis and personality disorders), but two inherent aspects to each disorder. It is essential to consider psychological and psychopathological aspects of psychoses, as well as the brain dysfunction of the variations of the psychic way of being.

The categorical perspective is deep rooted in the psychiatric tradition. Categorical models consider discontinuous personality categories. This type of model is used in DSM-IV⁽¹⁶⁾ and ICD-10⁽¹⁷⁾ because of the need for a specific diagnostic, i.e. a categorical approach.

In modern nosology the categorisation of illness is based on the symptoms present and not on their aetiopathology, and says nothing about the nature of the disorders themselves. In the case of personality disorders, the categorisation does not affirm or deny that they are disorders or illnesses, nor does it indicate where the symptoms differ from non-morbid behaviour patterns.

This approach is supported by the notion of ideal types of Weber (1864- 1920), introduced into psychiatry by Jaspers (1883-1969) and more recently by Schwartz and Wiggins.⁽¹⁸⁾ Ideal types are constructs to understand reality: An ideal type is formed by a unilateral accentuation of one or more perspectives and by the synthesis of a great deal of individual phenomena. A type describes the perfect case. Recently Doerr⁽¹⁹⁾ has argued that the ideal types, when well described, become almost real types.

The experimental approach looks for general laws on personality and establishes causal relations between personality variables. Wundt (1832-1920) studied the effects of modifications of stimuli on the intensity and quality of the subject’s experiences introduced them. Pavlov (1849-1936) studied the conditioning of the responses to stimuli and the experimental neurosis. The behavioural approach to the personality was introduced by Watson (1878-1958) who applied objective methods to the study of human behaviour and to the relationship between stimuli and responses. Hull (1884-1952) expanded behaviourism to include learning, feelings, expectations, achievements, goals and motivations. This led to the notion that the stimulus response relationship is influenced by cognitive processes. Perception, memory, language and other functions influence the processing of information of the surrounding world and the information coming from oneself (self). Skinner (1904-1990) created a theory of the operating conditioning, result of a non-adaptative learning. From these perspectives, the personality is viewed as a computer which introduces, stores, transforms and produces information, including the contents of the information as well as the process in itself.⁽²⁰⁾

Freud (1856-1939)⁽²¹⁾ proposed in the course of his life three different models of personality: The first was the speculative neuropsychological model of the Project of a psychology for neuropsychiatrists (1897) based on the concepts of psychic energy and psychodynamic. The second was the topographic model of the The Interpretation of Dreams (1900) where Freud described the conscious, preconscious and unconscious levels. The third is the structural model of The Ego and the Id (1923) and of Inhibition, Symptoms and Anxiety (1926) where Freud introduced the notions of the Id, the Ego and the Super-Ego. This last model led to a new perspective, the psychology of the Ego and the description of defence mechanisms which have a strong impact on the study of personality in clinical settings. Defence mechanisms distort reality to adapt the subject to it and to reduce anxiety. Some of them are more normal (promote adaptation to the environment), others are pathological (maladjusted or maladaptative).

The correlation approach explains the individual differences based on personality traits and applying a dimensional model based on statistical correlation. Karl Pearson (1857-1936), the founder of mathematical statistics introduced the correlation coefficient (correlates of cognitive flair with variables like age, gender, weight, height and so on). Charles E. Spearman (1863-1945) applied to research on the traits of personality, a factorial analysis that groups different qualities around a series of correlational factors or dimensions.

Traits are the basic elements of a personality and individual differences are defined and classified along dimensions. The theoretical assumption is that the structure of personality is common to all individuals; it differs in the different combination of traits. Trait is a disposition to respond in a determined way to a determined situation. Traits characterize persons through brief and precise descriptions on stable ways to behave, and as behaviour is consistent, it is possible to predict behaviours. This approach has paved the way to basic dimensions of individual differences.

Jung (1875-1961) made the first important contribution to the dimensional concept of the personality, based on the concept of trait or disposition.⁽²²⁾ A trait is a permanent inclination towards behaving in a determinant way. Traits are distributed along dimensions which make it possible to classify individuals according to their personality. The different dimensional models are based on the supposition that we all share the same personality structure, differing in the different combination of the mentioned traits. These models have benefited from the innovative statistic techniques, which allows to group different qualities of the individual character around factors of correlation or dimensions.

This dimensional approach raises several questions. How many traits define personality? Are the traits universal? Do traits relate only to manifest behaviours or are they part of feelings, values or thoughts? The problem of the number of dimensions that define personality led to the search for external validators such as biological, cultural and genetic factors. Eysenck⁽²³⁾ identified there are three basic types of personality: extroversion-introversion, neuroticism and psychoticism, each one including multiple levels of traits. For Eysenck and Eysenck,⁽²⁴⁾ the concept of arousal level is essential. Every individual has an optimal activation level of specific systems of the central nervous system—the better they feel, the better they will perform. This approach has been developed by many authors including Zuckermann,⁽²⁵⁾ who described sensation-seeking behaviour, Oreland et al.,⁽²⁶⁾ and Siever and Davis,⁽²⁷⁾ who proposed new traits and dimensions.

Cloninger⁽²⁸⁾ initially proposed three dimensions: novelty-seeking, harm avoidance, and reward dependence. Latter, he attempted to overcome the dichotomy between dimensional and categorical models by using four temperamental dimensions (novelty-seeking, harm avoidance, reward dependence, and persistence), which are life-long and stable, and three character dimensions (self-direction,
co-operation, and self-transcendency) which are variable and susceptible to environmental influences and development.⁽²⁹⁾

The five-factor model, based on factorial studies and individual differences⁽³⁰⁾ has been widely accepted. It comprises the personality dimensions openness, conscientiousness, extraversion, agreeableness, and neuroticism, known by the acronym OCEAN. About 40 per cent of individual personality differences can be explained in terms of heredity.⁽³¹⁾ In the five-factor model the same proportion does not apply to each factor; openness to experience appears to have the greatest hereditary input, whereas conscientiousness appears to have the least.

Mathematical tools allow recombining the data in order to find higher order factors of the Big Five. Two of them have appeared in many studies: 1) related to the Big Five trait dimensions Agreeableness, Conscientiousness, and Emotional Stability (meta-trait alpha) and 2) the dimensions Extraversion and Intellect (meta-trait beta).⁽³²⁾ Other have found some extra traits to be added to the Big Five, such as honesty-humility.⁽³³⁾

An interesting approach is lexicographic, which is based on the examination of relations among personality-descriptive adjectives that are indigenous to various languages. They tend to reveal a structure corresponding closely to the Five-Factor Model, with some differences in the nature of the Agreeableness and Emotionality/Neuroticism factors and also in the existence of a sixth factor, Honesty-Humility.⁽³⁴⁾ This has been found in different languages such a tagalong with some differences (a Filipino extra factor resembled a Negative Valence or Infrequency dimension).⁽³⁴⁾ A study with college students yielded seven major dimensions; many of the factors were similar to recognized lexical personality factors. Big Five Conscientiousness and Neuroticism were each strongly associated with a single proverb dimension (interpreted as Restraint and Enjoys Life, respectively). Big Five Agreeableness, Extraversion, and Intellect/Imagination were all associated with several proverb dimensions. Agreeableness was most strongly associated with proverb dimensions representing Machiavellian behaviour and strong Group Ties, and both Extraversion and Intellect showed particularly notable associations with an Achievement Striving dimension. The two remaining proverb dimensions, which represented a belief that Life is Fair and an attitude of Cynicism, could not be accounted for by the Big Five.⁽³⁵⁾