Paranoid personality disorder (PPD) is a mental disorder characterized by paranoia and a pervasive, long-standing suspiciousness and generalized mistrust of others. Individuals with this personality disorder may be hypersensitive, easily insulted, and habitually relate to the world by vigilant scanning of the environment for clues or suggestions that may validate their fears or biases. Paranoid individuals are eager observers. They think they are in danger and look for signs and threats of that danger, potentially not appreciating other evidence.

They tend to be guarded and suspicious and have quite constricted emotional lives. Their reduced capacity for meaningful emotional involvement and the general pattern of isolated withdrawal often lend a quality of schizoid isolation to their life experience. People with PPD may have a tendency to bear grudges, suspiciousness, tendency to interpret others' actions as hostile, persistent tendency to self-reference, or a tenacious sense of personal right. Patients with this disorder can also have significant comorbidity with other personality disorders.

Neurosis is a class of functional mental disorders involving chronic distress but neither delusions nor hallucinations. The term is no longer used by the professional psychiatric community in the United States, having been eliminated from the "Diagnostic and Statistical Manual of Mental Disorders" in 1980 with the publication of DSM III. It is still used in the .

Neurosis should not be mistaken for psychosis, which refers to a loss of touch with reality. Neither should it be mistaken for neuroticism, a fundamental personality trait proposed in the big Five personality traits theory.

Pan-Neurosis is the existence of multiple neurotic symptoms such as:

- obsessions

- compulsions

- phobias

- hysteria

- depression

- hypochondriasis

- depersonalization

Diffuse anxiety is stimulated by a minor catalyst and may persist long after the catalyst disappears.

The World Health Organization's ICD-10 lists paranoid personality disorder as "() Paranoid personality disorder".

It is a requirement of ICD-10 that a diagnosis of any specific personality disorder also satisfies a set of general personality disorder criteria. It is also pointed out that for different cultures it may be necessary to develop specific sets of criteria with regard to social norms, rules and other obligations.

According to psychoanalytic theory, neuroses may be rooted in ego defense mechanisms, but the two concepts are not synonymous. Defense mechanisms are a normal way of developing and maintaining a consistent sense of self (i.e., an ego). But only those thoughts and behaviors that produce difficulties in one's life should be called neuroses.

A neurotic person experiences emotional distress and unconscious conflict, which are manifested in various physical or mental illnesses. The definitive symptom is anxiety.

Neurotic tendencies are common and may manifest themselves as acute or chronic anxiety, depression, an obsessive–compulsive disorder, a phobia, or a personality disorder.

Some debates have pervaded the field of psychology since its genesis. Perhaps one of the most salient ones deals with the nature of personality. Personality psychology studies one's distinctive style of cognition, behavior, and affect. However, this concept elicits discord among psychologists as some have insisted that it does not exist, while others struggle with issues of measurement.

Ideas of reference and delusions of reference describe the phenomenon of an individual's experiencing innocuous events or mere coincidences and believing they have strong personal significance. It is "the notion that everything one perceives in the world relates to one's own destiny".

In psychiatry, delusions of reference form part of the diagnostic criteria for psychotic illnesses such as schizophrenia, delusional disorder, bipolar disorder (during the elevated stages of mania), as well as schizotypal personality disorder. To a lesser extent, it can be a hallmark of paranoid personality disorder. Such symptoms can also be caused by intoxication, especially with hallucinogens or stimulants like methamphetamine.

Cluster B personality disorders are a categorization of personality disorders as defined in the DSM-IV and DSM-5.

Cluster B personality disorders are characterized by dramatic, overly emotional or unpredictable thinking or behavior and manipulative, exploitative interactions with others. They include antisocial personality disorder, borderline personality disorder, histrionic personality disorder and narcissistic personality disorder.

The British National Health Service has described those with this disorder as someone who, "struggles to relate to others. As a result, they show patterns of behaviour most would regard as dramatic, erratic and threatening or disturbing."

There are four recognized Cluster B personality disorders:

- Antisocial personality disorder (DSM-IV code 301.7): a pervasive disregard for the law and the rights of others.

- Borderline personality disorder (DSM-IV code 301.83): extreme "black and white" thinking, instability in relationships, self-image, identity and behavior often leading to self-harm and impulsivity.

- Histrionic personality disorder (DSM-IV code 301.50): pervasive attention-seeking behavior including inappropriately seductive behavior and shallow or exaggerated emotions.

- Narcissistic personality disorder (DSM-IV code 301.81): a pervasive pattern of grandiosity, need for admiration, and a lack of empathy.

Perfectionism, in psychology, is a personality trait characterized by a person's striving for flawlessness and setting high performance standards, accompanied by critical self-evaluations and concerns regarding others' evaluations. It is best conceptualized as a multidimensional characteristic, as psychologists agree that there are many positive and negative aspects. In its maladaptive form, perfectionism drives people to attempt to achieve an unattainable ideal, while their adaptive perfectionism can sometimes motivate them to reach their goals. In the end, they derive pleasure from doing so. When perfectionists do not reach their goals, they often fall into depression.

A monothematic delusion is a delusional state that concerns only one particular topic. This is contrasted by what is sometimes called "multi-thematic" or "polythematic" delusions where the person has a range of delusions (typically the case of schizophrenia). These disorders can occur within the context of schizophrenia or dementia or they can occur without any other signs of mental illness. When these disorders are found outside the context of mental illness, they are often caused by organic dysfunction as a result of traumatic brain injury, stroke, or neurological illness.

People who experience these delusions as a result of organic dysfunction often do not have any obvious intellectual deficiency nor do they have any other symptoms. Additionally, a few of these people even have some awareness that their beliefs are bizarre, yet they cannot be persuaded that their beliefs are false.

A self-disorder, also called ipseity disturbance, is a psychological phenomenon of disruption or diminishing of a person's sense of minimal (or basic) self. The sense of minimal self refers to the very basic sense of having experiences that are one's own; it has no properties, unlike the more extended sense of self, the narrative self, which is characterized by the person's reflections on themselves as a person, things they like, their identity, and other aspects that are the result of reflection on one's self. Disturbances in the sense of minimal self, as measured by the Examination of Anomalous Self-Experience (EASE), aggregate in the schizophrenia spectrum disorders, to include schizotypal personality disorder, and distinguish them from other conditions such as psychotic bipolar disorder and borderline personality disorder.

Schizotypal personality disorder (STPD) or schizotypal disorder is a mental disorder characterized by severe social anxiety, thought disorder, paranoid ideation, derealization, transient psychosis, and often unconventional beliefs. People with this disorder feel extreme discomfort with maintaining close relationships with people, mainly because they think that their peers harbor negative thoughts towards them, so they avoid forming them. Peculiar speech mannerisms and odd modes of dress are also symptoms of this disorder. Those with STPD may react oddly in conversations, not respond or talk to themselves.

They frequently interpret situations as being strange or having unusual meaning for them; paranormal and superstitious beliefs are common. Such people frequently seek medical attention for anxiety or depression instead of their personality disorder. Schizotypal personality disorder occurs in approximately 3% of the general population and is more common in males.

The term ""schizotype"" was first coined by Sandor Rado in 1956 as an abbreviation of ""schizophrenic phenotype"". STPD is classified as a cluster A personality disorder ("odd or eccentric disorders") and is considered to be the most impairing disorder in this cluster.

The delusions that fall under this category are:

- Capgras delusion: the belief that (usually) a close relative or spouse has been replaced by an identical-looking impostor.

- Fregoli delusion: the belief that various people whom the believer meets are actually the same person in disguise.

- Intermetamorphosis: the belief that people in one's environment swap identities with each other while maintaining the same appearance.

- Subjective doubles: a person believes there is a doppelgänger or double of him- or herself carrying out independent actions.

- Cotard delusion: the belief that oneself is dead or does not exist; sometimes coupled with the belief that one is putrefying or missing internal organs.

- Mirrored-self misidentification: the belief that one's reflection in a mirror is some other person.

- Reduplicative paramnesia: the belief that a familiar person, place, object, or body part has been duplicated. For example, a person may believe that they are, in fact, not in the hospital to which they were admitted, but in an identical-looking hospital in a different part of the country.

- Somatoparaphrenia: the delusion where one denies ownership of a limb or an entire side of one's body (often connected with stroke).

Note that some of these delusions are sometimes grouped under the umbrella term of delusional misidentification syndrome.

The Diagnostic and Statistical Manual of Mental Disorders revision IV (DSM-IV) describes passive–aggressive personality disorder as a "pervasive pattern of negativistic attitudes and passive resistance to demands for adequate performance in social and occupational situations."

Passive-aggressive behavior is the obligatory symptom of the passive–aggressive personality disorder. Persons with passive–aggressive personality disorder are characterized by procrastination, covert obstructionism, inefficiency and stubbornness.

In the American Psychiatric Association's DSM-5, schizotypal personality disorder is defined as a "pervasive pattern of social and interpersonal deficits marked by acute discomfort with, and reduced capacity for, close relationships as well as by cognitive or perceptual distortions and eccentricities of behavior, beginning by early adulthood and present in a variety of contexts."

At least five of the following symptoms must be present: ideas of reference, strange beliefs or magical thinking, abnormal perceptual experiences, strange thinking and speech, paranoia, inappropriate or constricted affect, strange behavior or appearance, lack of close friends, and excessive social anxiety that does not abate and stems from paranoia rather than negative judgments about self. These symptoms must not occur only during the course of a disorder with similar symptoms (such as schizophrenia or autism spectrum disorder).

The 10th revision of the International Classification of Diseases (ICD-10) of the World Health Organization (WHO) includes passive–aggressive personality disorder in the "other specific personality disorders" rubric (description: "a personality disorder that fits none of the specific rubrics: F60.0–F60.7"). ICD-10 code for "other specific personality disorders" is . For this psychiatric diagnosis a condition must meet the general criteria for personality disorder listed under F60 in the clinical descriptions and diagnostic guidelines.

The general criteria for personality disorder includes markedly disharmonious behavior and attitudes (involving such areas of functioning as affectivity – ability to experience affects: emotions or feelings, involving ways of perceiving and thinking, impulse control, arousal, style of relating to others), the abnormal behavior pattern (enduring, of long standing), personal distress and the abnormal behavior pattern must be clearly maladaptive and pervasive. Personality disorder must appear during childhood or adolescence and continue into adulthood.

Specific diagnostic criteria of the passive–aggressive personality disorder in the "Diagnostic criteria for research" by WHO is not presented.

In considering whether an individual has thought disorder, patterns of their speech are closely observed. Although it is normal to exhibit some of the following during times of extreme stress (e.g. a cataclysmic event or the middle of a war) it is the degree, frequency, and the resulting functional impairment that leads to the conclusion that the person being observed has a thought disorder.

- "Alogia" (also "poverty of speech") – A poverty of speech, either in amount or content; it can occur as a negative symptom of schizophrenia.

- "Blocking" – An abrupt stop in the middle of a train of thought; the individual may or may not be able to continue the idea. This is a type of formal thought disorder that can be seen in schizophrenia.

- "Circumstantiality" (also "circumstantial thinking", or "circumstantial speech") – An inability to answer a question without giving excessive, unnecessary detail. This differs from tangential thinking, in that the person does eventually return to the original point.

- "Clanging" or "Clang association" – a severe form of flight of ideas whereby ideas are related only by similar or rhyming sounds rather than actual meaning. This may be heard as excessive rhyming and/or alliteration. e.g. "Many moldy mushrooms merge out of the mildewy mud on Mondays." "I heard the bell. Well, hell, then I fell." It is most commonly seen in bipolar affective disorder (manic phase), although it is often observed in patients with primary psychoses, namely schizophrenia and schizoaffective disorder.

- "Derailment" (also "loose association" and "knight's move thinking") – Thought and/or speech move, either spontaneously or in response to an internal stimulus (distinguishing derailment from "distractible speech," "infra"), from the topic's track onto another which is obliquely related or unrelated. e.g. "The next day when I'd be going out you know, I took control, like uh, I put bleach on my hair in California."

- "Distractible speech" – During mid speech, the subject is changed in response to an external stimulus. e.g. "Then I left San Francisco and moved to... where did you get that tie?"

- "Echolalia" – Echoing of another's speech that may only be committed once, or may be continuous in repetition. This may involve repeating only the last few words or last word of the examiner's sentences. This can be a symptom of Tourette's Syndrome. e.g. "What would you like for dinner?", "That's a good question. "That's a good question". "That's a good question". "That's a good question"."

- "Evasive interaction" – Attempts to express ideas and/or feelings about another individual come out as evasive or in a diluted form, e.g.: "I... er ah... you are uh... I think you have... uh-- acceptable erm... uh... hair."

- "Flight of ideas" – a form of formal thought disorder marked by abrupt leaps from one topic to another, albeit with discernable links between successive ideas, perhaps governed by similarities between subjects or, in somewhat higher grades, by rhyming, puns, and word plays (clang associations), or innocuous environmental stimuli – e.g., the sound of birds chirping. It is most characteristic of the manic phase of bipolar illness.

- "Illogicality" – Conclusions are reached that do not follow logically (non-sequiturs or faulty inferences). e.g. "Do you think this will fit in the box?" draws a reply like "Well duh; it's brown, isn't it?"

- "Incoherence (word salad)" – Speech that is unintelligible because, though the individual words are real words, the manner in which they are strung together results in incoherent gibberish, e.g. the question "Why do people comb their hair?" elicits a response like "Because it makes a twirl in life, my box is broken help me blue elephant. Isn't lettuce brave? I like electrons, hello please!"

- "Loss of goal" – Failure to follow a train of thought to a natural conclusion. e.g. "Why does my computer keep crashing?", "Well, you live in a stucco house, so the pair of scissors needs to be in another drawer."

- "Neologisms" – New word formations. These may also involve elisions of two words that are similar in meaning or in sound. e.g. "I got so angry I picked up a dish and threw it at the geshinker."

- "Perseveration" – Persistent repetition of words or ideas even when another person attempts to change the topic. e.g. "It's great to be here in Nevada, Nevada, Nevada, Nevada, Nevada." This may also involve repeatedly giving the same answer to different questions. e.g. "Is your name Mary?" "Yes." "Are you in the hospital?" "Yes." "Are you a table?" "Yes." Perseveration can include palilalia and logoclonia, and can be an indication of organic brain disease such as Parkinson's.

- "Phonemic paraphasia" – Mispronunciation; syllables out of sequence. e.g. "I slipped on the lice and broke my arm."

- "Pressure of speech" – Unrelenting, rapid speech without pauses. It may be difficult to interrupt the speaker, and the speaker may continue speaking even when a direct question is asked.

- "Self-reference" – Patient repeatedly and inappropriately refers back to self. e.g. "What's the time?", "It's 7 o'clock. That's my problem."

- "Semantic paraphasia" – Substitution of inappropriate word. e.g. "I slipped on the coat, on the ice I mean, and broke my book."

- "Stilted speech" – Speech characterized by the use of words or phrases that are flowery, excessive, and pompous. e.g. "The attorney comported himself indecorously."

- "Tangentiality" – Wandering from the topic and never returning to it or providing the information requested. e.g. in answer to the question "Where are you from?", a response "My dog is from England. They have good fish and chips there. Fish breathe through gills."

- "Word approximations" – Old words used in a new and unconventional way. e.g. "His boss was a ."

In psychology, relationship obsessive–compulsive disorder (ROCD) is a form of obsessive-compulsive disorder focusing on intimate relationships (whether romantic or non-romantic). Such obsessions can become extremely distressing and debilitating, having negative impacts on relationships functioning.

Thought disorder (TD) or formal thought disorder (FTD) refers to disorganized thinking as evidenced by disorganized speech. Specific thought disorders include derailment, poverty of speech, tangentiality, illogicality, perseveration, and thought blocking.

Psychiatrists consider formal thought disorder as being one of two types of disordered thinking, with the other type being delusions. The latter involves "content" while the former involves "form". Although the term "thought disorder" can refer to either type, in common parlance it refers most often to a disorder of thought "form" also known as formal thought disorder.

Eugen Bleuler, who named schizophrenia, held that thought disorder was its defining characteristic. However, formal thought disorder is not unique to schizophrenia or psychosis. It is often a symptom of mania, and less often it can be present in other mental disorders such as depression. Clanging or echolalia may be present in Tourette syndrome. Patients with a clouded consciousness, like that found in delirium, also have a formal thought disorder.

However, there is a clinical difference between these two groups. Those with schizophrenia or psychosis are less likely to demonstrate awareness or concern about the disordered thinking. Clayton and Winokur have suggested that this results from a fundamental inability to use the same type of Aristotelian logic as others. On the other hand, patients with a clouded consciousness, referred to as "organic" patients, usually do demonstrate awareness and concern, and complain about being "confused" or "unable to think straight"; Clayton and Winokur suggest that this is because their thought disorder results, instead, from various cognitive deficits.

Thought insertion is defined by the ICD-10 as feeling as if one's thoughts are not one's own, but rather belong to someone else and have been inserted into one's mind. The person experiencing thought insertion will not necessarily know where the thought is coming from, but is able to distinguish between their own thoughts and those inserted into their minds. However, patients do not experience all thoughts as inserted, only certain ones, normally following a similar content or pattern. This phenomenon is classified as a delusion. A person with this delusional belief is convinced of the veracity of their beliefs and is unwilling to accept such diagnosis.

Thought insertion is a common symptom of psychosis and occurs in many mental disorders and other medical conditions. However, thought insertion is most commonly associated with schizophrenia. Thought insertion, along with thought broadcasting, thought withdrawal, thought blocking and other first rank symptoms, is a primary symptom and should not be confused with the delusional explanation given by the respondent. Although normally associated with some form of psychopathology, thought insertion can also be experienced in those considered nonpathological, usually in spiritual contexts, but also in culturally influenced practices such as mediumship and automatic writing.

Examples of thought insertion:

"She said that sometimes it seemed to be her own thought 'but I don't get the feeling that it is'. She said her 'own thoughts might say the same thing', 'but the feeling isn't the same', 'the feeling is that it is somebody else's'"

"I look out the window and I think that the garden looks nice and the grass looks cool, but the thoughts of Eamonn Andrews come into my mind. There are no other thoughts there, only his. He treats my mind like a screen and flashes thoughts onto it like you flash a picture"

"The subject has thoughts that she thinks are the thoughts of other people, somehow occurring in her own mind. It is not that the subject thinks that other people are making her think certain thoughts as if by hypnosis or psychokinesis, but that other people think the thoughts using the subject's mind as a psychological medium."

The presence of self-disorders may have predictive power for whether those with an at risk mental state will develop psychosis; the risk of suicidal ideation and suicide by people with schizophrenia, though depression would also be an important factor; predicting initial social dysfunction in people with either schizophrenic or bipolar psychosis; and whether a person will move to a schizophrenia spectrum diagnosis later.

The presence of self-disorders may cause reduced person insight into their illness through the alteration of the basic structures of consciousness.

Self-disorders are difficult for the people experiencing them to articulate spontaneously; and are not well-known, by either the general public or professionals in the field. Because of this, people will often make vague, cliched complaints that mimic the symptoms of other mental disorders, symptoms such as "fatigue" or "concentration difficulties". Were a knowledgeable clinician to probe deeper, however, the underlying self-disorders may be assessed and help clarify the nature of the person's illness. In their review, Parnas, et al. (2014) say, "The psychiatrist’s acquaintance with the phenomenon of 'non-specific specificity' is, in our view, extremely important in the context of early diagnostic assessment, especially of people presenting with a vague, unelaborated picture of maladjustment, underperformance, chronic malaise and dysphoria, negative symptoms, or hypochondriac preoccupations." People with schizophrenia often describe their self-disorders as causing more suffering for them than psychosis.

Self-disorders underlie most of the first-rank symptoms, those often termed passivity phenomena. There is a current proposal to list self-disorder as one of the symptoms of schizophrenia in the upcoming ICD-11.

Persons with ideas of reference may experience:

- Believing that 'somehow everyone on a passing city bus is talking about them, yet they may be able to acknowledge this is unlikely'.

- A feeling that people on television or radio are talking about or talking directly to them

- Believing that headlines or stories in newspapers are written especially for them

- Believing that events (even world events) have been deliberately contrived for them, or have special personal significance for them

- Believing that the lyrics of a song are specifically about them

- Believing that the normal function of cell phones, computers, and other electronic devices are sending secret and significant messages that only they can understand or believe.

- Seeing objects or events as being set up deliberately to convey a special or particular meaning to themselves

- Thinking 'that the slightest careless movement on the part of another person had great personal meaning...increased significance'.

- Thinking that posts on social network websites or Internet blogs have hidden meanings pertaining to them.

- Believing that the behavior of others is in reference to an abnormal, offensive body odor, which in reality is non-existent and cannot be detected by others (see: olfactory reference syndrome).

Perfectionists strain compulsively and unceasingly toward unobtainable goals, and measure their self-worth by productivity and accomplishment. Pressuring oneself to achieve unrealistic goals inevitably sets the person up for disappointment. Perfectionists tend to be harsh critics of themselves when they fail to meet their standards.

Obsessive-compulsive disorder comprises thoughts, images or urges that are unwanted, distressing, interfere with a person's life and that are commonly experienced as contradicting a persons' beliefs and values. Such intrusive thoughts are frequently followed by compulsive behaviors aimed at "neutralizing" the feared consequence of the intrusions and temporarily relieve the anxiety caused by the obsessions. Attempts to suppress or "neutralize" obsessions increase rather than decrease the frequency and distress caused by the obsessions.

Common obsessive themes include fear of contamination, fears about being responsible for harming the self or others, doubts, and orderliness. However, people with OCD can also have religious and sexual obsessions. Some people with OCD may experience obsessions relating to the way they feel in an ongoing relationship or the way they felt in past relationships (ROCD). Repetitive thought about a person's feelings in intimate relationships may occur in the natural course of the relationship development; however, in ROCD such preoccupations are unwanted, intrusive, chronic and disabling.