It is clear that the current paradigm about the nature of mental illness is that of conceptualizing it in terms of a type of disease:

“What psychiatrists describe as ‘mental illnesses’ are diseases that are causally explained by their underlying pathophysiology. It is committed to specific causal hypotheses in terms of abnormalities in underlying neurobiological systems, which are responsible for the observed patterns of signs and symptoms.” (Murphy, 968)

And:

“An explanation of mental illness will ultimately cite destructive processes in brain systems, just as bodily diseases are explained by such processes in other organs. The process can mediate the effects of cultural forces or other environmental risk factors. Nor does the cause of a disorder have to completely destroy a brain system: it may be enough to put the system into a stable but chronically dysregulated state…[there are], in psychiatry, phenomena that fit the conception of disease as a destructive process realized in bodily organs that predominates in biomedicine generally” (Murphy, 968).

In common english vernacular, the words “disorder”, “disease”, and “illness” are often used interchangeably. However, in the neurosciences and medicine more generally these words have different uses. A “disorder” refers to a malfunction of a biological process or organ when there is no known pathology. If the purpose of a kidney is to remove waste and extra fluid from our blood, then a kidney that is no longer able to remove waste or extra fluid is suffering from a malfunction and is therefore a type of disorder. Disorders can be caused by genetics, disease, or trauma. A disease or illness on the other hand refers to actually known pathophysiological processes. Hence the claim about the causes of disorders: there are many, with illnesses/diseases being just one type of cause.

Why this brief terminological digression? Because as we have seen above, the psychiatric profession continues to use the terms “mental illness” and “mental disorder” interchangeably, thereby obscuring the important distinction that unless the pathology of a mental condition is known, it cannot be called or said to be caused by an “illness”. But biomedical model proponents blur these distinctions, merely asserting that the 200+ disorders found in the DSM are rooted in biological illnesses without discovering the pathology of any of them to date.

I grant that some disorders may, but it does not follow that all of them will. The declaration, before the biological pathologies are even established, that they either are illnesses or are caused by them is an ideological pronouncement, not an empirical finding. The biomedical model’s prediction of what we should expect to find about the causes of mental health conditions is instead asserted as what has already been established.

There are two key takeaways from this: the biomedical model is concerned with asking and providing answers to the following questions:

What is a mental disorder?

It’s a medical disease of the human brain.

What causes mental illness?

Destructive or dysregulating processes in brain systems.

Notice the confusion here. As seen above, disorders are typically understood to be caused by disease, but biomedical proponents fluctuate between claiming mental disorders are diseases and subtly talk about them being caused by illnesses instead. This terminological confusion is no doubt responsible for the intractability of the debate.

The biomedical model concerns itself with providing an explanation for both the nature and causes of mental illness. Just as cancer is understood to be a term for diseases in which abnormal cells divide without control and can invade nearby tissues, mental illness is a term for diseases in which certain dysfunctions of brain processes lead to the destruction or dysregulation of brain systems.

It is paramount to note that this is where the biomedical model diverges from the biopsychosocial: in giving us an account of the nature and causes of mental illness, the biomedical model will ultimately provide an explanation that is mechanistic. The ultimate aim is to show how the parts of a system (the brain) possess certain structures and activities which give rise to (cause or produce) the phenomena in question. It is a reductionist account that explains the nature of mental illness by appealing to underlying processes within that system itself.

By contrast, the biopsychosocial model eschews the reductionist approach by appealing to factors external to the brain that play an equally important role in the development of mental health disorders. External factors such as child abuse, the state of one’s marriage, history of substance abuse, as well as stressful environmental events like unemployment or bereavement (Murphy, 974). The objection is that by focusing our attention and research on causal factors within the brain, we are neglecting equally important links in the causal chain without which a complete explanation will be impossible.

Notice that whereas cancer is defined in terms of its causes, as in when the “body’s cells begin to divide without stopping and spread into surrounding tissues”, we do not yet know the specific causes for most of the mental illnesses found within the DSM. Therefore, “destruction or dysregulation of brain systems” is understood to be a placeholder causal definition of mental disorders until the specific underlying neurobiological mechanisms that give rise to these disorders are identified.

Until the underlying causal pathways for disorders such as schizophrenia are found, the biomedical model cannot define individual disorders by means of their actual known causes, as we do with cancer. This is so because psychiatry has yet to find any simple biological cause for any major mental disorder (Deacon, 856). As former head of the National Institute for Mental Health Thomas Insel writes regarding the DSM and psychiatry’s current nosology: