Every human is unique. In addition to physical differences, we each have individual psychological characteristics, such as personality and intelligence, that make us recognizably different from other people. But there are some things that most of us have in common—things we consider to be “normal.”

Finding fault

We recognize normality in many aspects of day-to-day life, and tend to avoid things that we consider “abnormal.” Even when buying carrots, we naturally prefer the more carrotlike ones.

What is abnormal?

We may have a good idea of what we consider to be normal, but it’s not easy to define exactly what we mean by normality. Behavior that is considered normal in one culture may be deemed strange in another, and we each have our own ideas of what is normal. One way of trying to define normal is to look at what we consider to be abnormal. This could be simply behavior that is different from how most people behave—yet the word abnormal also suggests that something is undesirable or unacceptable. People with special talents, for example, are not seen as abnormal, but exceptional. When we label people as abnormal, we are saying that they are not as we think they should be. Just as we have an idea of physical health, we measure people by an idea of normal mental health, and tend to describe those who deviate from this as having a mental disorder or illness. And because we see those people as different, there is often a stigma attached to mental disorders.

Classifying mental disorders

In medieval times, abnormal behavior was thought to be caused by witchcraft, but, as science progressed, attitudes changed, and it became regarded more as a type of disease. Psychiatry emerged in the 19th century as a branch of medicine to offer treatment for mental illness (although modern psychologists prefer to think in terms of mental disorders, rather than illness). One of the pioneers of psychiatry, Emil Kraepelin, believed that mental illness had physical causes, like any other disease. He identified two types of mental illness: manic-depressive psychosis (now known as mood or affective disorder), caused by external conditions and therefore curable; and dementia praecox (now called schizophrenia), caused by physical problems in the brain that were incurable. His classification was the first of its kind, and formed the basis for modern systems of classifying various mental disorders, such as the World Health Organization’s International Classification of Diseases (ICD), and the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders (DSM). Both list disorders stemming from brain disease or damage, schizophrenia, substance abuse disorders, mood disorders, anxiety disorders, personality and behavioral disorders, and eating and sleeping disorders.

Problems in living

Not all psychologists agree with labeling so-called “abnormal” behaviors as medical conditions that require treatment. One critic of this practice was Thomas Szasz, who believed that unless there is a physical cause such as brain damage, mental disorders should be considered not as illnesses, but as “problems in living” resulting from things that ordinary people have to deal with in everyday life, such as the end of a relationship or the death of a relative. In his view, many of the conditions psychiatrists describe as mental disorders, including depression and anxiety, are in fact a normal part of human life. Although this is an extreme view, most psychiatrists and psychologists recognize that there is a difference between organic mental disorders (those with a physical cause) and functional disorders (those that Szasz has described as “problems in living”).

In the Middle Ages, people who behaved in an unusual way were thought to be possessed by demons.

See also: Are you INSANE? | Is therapy the ANSWER?