A more difficult question to answer than one might think. As usual your definition depends on all or some of: your point of view, how deeply you wish to probe, how many people are sitting on your committee and how long you’ve got to write it before you break for lunch.
Before I get stuck in, it’s worth noting that the term ‘health’ is a non-exact term used loosely in everyday speech. Equally ‘mental health’, ‘mental illness’ and ‘mental disorder’ are used with an comparable lack of precision and the latter two most often interchangeably. In addition psychiatric health/illness/disorder are used synonymously with mental health/illness/disorder. A further problem with this concept is that there is no clear cut off point between mental disorder and mental health; indeed one person’s mental health, might be another’s mental disorder.
With this poverty of precision already built in, it is probably unfair to expect too much. For this posting I will be mostly using the phrase ‘mental disorder’. Whatever their definitions, common sense dictates that ‘mental health’ and ‘mental illness’ are at least related such that as one increases, the other decreases. There is no definition of mental disorder which is either entirely satisfactory or uniformly accepted.
For legal purposes, the UK’s Mental Health Act 2007 defines mental disorder succinctly and thusly:
‘Mental disorder’ means any disorder or disability of the mind (page 7)
It is clear here, even to the casual reader, is that there is a marked circularity to this statement. Verbose as ever the World Health Organisation makes the following submission:
Mental health can be conceptualized as a state of well-being in which the individual realizes his or her own abilities, can cope with the normal stresses of life, can work productively and fruitfully, and is able to make a contribution to his or her community.
Furthermore they state emphatically:
Mental health is more than the absence of mental disorders (read the rest)
Inspiration for the definition of mental disorder often comes from the world of general medicine. Whether or not a mental disorder can or should be considered in the same way as, say, a viral illness is a discussion for another day but it is a direction that modern psychiatry is wedded to. Looked at this way mental disorder can be:
An absence of mental health.
A stumbling block here is that health is at least as difficult to define as illness. Always willing to have a bash, the WHO have defined ‘health’ as ‘a state of complete physical, social and mental well-being and not merely an absence of disease or infirmity’.
A presence of significant psychopathology.
This is related to the definition ‘disease is what doctors treat’, in that psychopathology would be identified by a nominated professional (but with their own distinct gaze…). It is another rather circular argument which allows for expansion of the concept which it describes, as when treatments become available for a condition it is more likely to be considered a disease (think of depression).
Similar to defining mental disorder as the presence of psychopathology is the wish to define mental disorder as the ‘presence of suffering’. This defines the group of people most likely to consult doctors, or other health care professionals. However unlike the definition relying on psychopathology, it leaves out people with mental disorders whose main effect is not felt by the sufferer at the time, for example during the manic phase of bipolar disorder or schizophrenia without insight.
Finally depending on our agenda, we can also choose to define mental illness out of existence. Enter the philosopher and anti-psychiatrist Thomas Szasz who wished to define a disease purely in terms of its physical pathology. Since most mental disorders do not have any demonstrable physical pathology, they are by this yardstick not illnesses. Although not sunk, this view has come under considerable attack from research which suggests genetic and neurobiological processes are involved in the aetiology of mental illness.