I want to argue, using the biopsychosocial model that, for any case of psychosis, we cannot, currently, say for sure what the ultimate cause of it is.
The biopsychosocial model can be thought of as both a theory of causes, and a theory of treatment. When thought of as a theory of causes, one looks at biological, psychological, and social factors involved in the development of psychosis.
We may find that, for example, there’s excessive pruning of neurons in the brains of most people with schizophrenia. But we may not know why that happens. It could be they are born prone to developing psychosis. It could be they are neurotypical, and have experienced a lot of hardship. It could be that, psychologically, they are vulnerable to stressors.
These can all be causes, and they can all contribute to one developing psychosis. For any individual person, they may not know what caused their own psychosis.
Think of global warming. We know that the Earth is warming at alarming rates. But, at any given place, it may be warmer or cooler. Just because one area experiences warmth or cooling doesn’t mean we can assign this to global warming. Global warming is an effect that is broad, and covers the entire Earth.
In the same way, psychosis may affect individuals, but each individual has had a different upbringing, social environment, experiences, and each individual reacts to their environment in different ways.
For some people, the biomedical explanation may be sufficient. For others, however, we may need to look at social and psychological factors. Teasing apart causes in any particular case would be difficult, and that’s more the job of clinicians and case managers, who are “on the ground” and working with the client.
As for me, when I look at data, I am looking at groups of people, and making connections. I may be focusing on social causes at the moment, but that doesn’t mean I don’t think other causes may be involved in particular cases.