Defining mental illness is categorically difficult. Knowing a few facts about how those definitions and diagnoses are arrived at can help a layperson understand exactly what kind of issues are at stake, and how to address and deal with an individual struggling with a certain disorder. 

The current manual of psychiatric disorder is the DSM-IV-TR (Diagnostic and Statistical Manual IV, text revision). The next version, the DSM-5, is currently being finalized, and will be released later this year; it is expected to include some definitive changes, but the four definitions here are adapted from the current manual. Schizophrenia begins the list, as the most often misunderstood of mental disorders.
  • Two or more of the following symptoms, not caused by manic or depressive episodes (explained below), persisting for at least one month at a time and repeatedly for at least six months.  
  1. Delusions (if bizarre, this is the only symptom required)
  2. Hallucinations (again, if persistent and severe, only this symptom is required)
  3. Disorganized speech - incoherence, connecting unrelated ideas (derailment)
  4. Extremely disorganized, or catatonic physical behavior
  5. Negative symptoms: loss of emotional range (flat affect), verbal range (alogia), or drive to accomplish goals (avolition).
  • These symptoms cause significant impairment in important areas of life, such as job performance and social interactions. They are not due to any medication or drug use, or restricted to the symptoms of a developmental disorder.

Generalized Anxiety Disorder: 
  • Excessive anxiety and worry, occurring more days than not for at least 6 months, about multiple things.
  • Difficulty controlling the worry, which causes significant impairment in important areas of life and functioning.
  • At least three of these six physical symptoms are present: restlessness, fatigue, difficulty concentrating, irritability, muscle tension, and sleep disturbance.
  • The worry is not due directly to some other disorder or substance abuse. 

Major Depressive Episode:
  • Five or more of the following symptoms must be present nearly every day for more than two weeks:
  1. Depressed mood: tearful, sad, or empty
  2. diminished interest or pleasure in normal activities 
  3. significant increase or decrease in weight or appetite
  4. Changed sleep patterns: consistently sleeping much more or much less than usual 
  5. changes in motor behavior - slower or faster movement than usual
  6. fatigue or loss of energy
  7. feelings of worthlessness or excessive guilt
  8. increased difficulty thinking, concentrating, or making decisions 
  9. recurring thoughts of death and suicide, up to and including suicide attempts

  • These cannot be explained by a recent bereavement, physical illness or condition, or drug or medication use, and cause significant impairment in functioning.

Bipolar Disorder:
  •  Major depressive episodes (as described above) alternate with manic episodes.  Manic episodes are severe enough to cause impairment in professional, social, or relational functioning, can include psychotic* features, and are not due to medication or drug use.  Episodes are characterized by three or more of these:
  1. persistent and abnormally elevated, expansive, or irritable mood
  2. inflated self-esteem or grandiose ideas
  3. decreased need for sleep
  4. increased talking, or need to continue talking more than usual
  5. racing thoughts or ideas
  6. distractability
  7. unusual increase in work towards specific goals
  8. Increase in risky, pleasurable activities - i.e., spending sprees, sexual misconduct, rash business decisions)

These definitions are by no means meant to encapsulate or define a person or their illness.  The textbook "Abnormal Psychology: an integrative approach" defines them as a "classification system for abnormal behavior" (p. 69 in my 4th edition copy). If a person exhibits these symptoms and concepts, they can reliably be diagnosed with a certain disorder, because those are the sorts of abnormal behaviors that are generally found to go together in certain types of people. 

This all happens on a spectrum. The best way I've seen to categorize it is the diathesis-stress model, which posits that clinical disorder is really more of a breaking point - the point where your applicable stress level meets your chemical and genetic predisposition to a certain behavior or trait and pushes you over the limit of normalcy.  So you can be almost at the breaking point, exhibiting some symptoms but not enough to be diagnosable, and still have some problems coping and getting by.  Generally, the point at which a person becomes diagnosable is the point at which their pathology starts seriously hindering their ability to function. Thhe definitions are simply a way to quantify whether someone has enough problems to justify intervention, and they are used accordingly as diagnostic tools, not as ways to define an individual.

I hope this is helpful - it's nice to know what someone is talking about when they say 'schizophrenic' or 'bipolar', and know what parts of those disorders make it difficult for someone to live their life normally, either on or off the streets.


*Psychosis is merely the loss of contact with reality. Any false perceptions about reality or the world - i.e., hearing voices, thinking the government is out to get you, thinking all your friends are angry with you, if none of those are true - are psychoses.  This is not exactly what the term means colloquially, so it's worth clarifying. 

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