Objective: To explore the limitations of the concept of 'truth' in the ontology of evidence-based psychiatry and to provide expanded ontological foundations for psychiatric practice based instead on the ontology of the French existential-phenomenologist, Maurice Merleau-Ponty.
Conclusions: Evidence-based medicine is founded on a 'scientific' ontology of 'causality', which equates 'truth' with effecting statistically-significant changes in objective measures of disease by a specified treatment. Because of the absence of biological markers of disease in psychiatry, evidence-based psychiatry equates 'truth' with effecting changes in observable psychometric measures of behaviour. This is the same ontology underlying marketing 'spin' and all attempts to effect pre-determined behavioural change. In contrast, Merleau-Ponty's ontology rejects causality and mind/body duality, and views 'truth' as the expression of our deepest embodied feeling and perception of the world, which establishes all our thinking, and on which all our thinking relies, including 'scientific' thinking. Merleau-Ponty's ontology is therefore a preferable foundation for psychiatric practice, because it allows psychiatrists to consider the 'truth' of clinically important, but non-measurable, aspects of psychiatry while not excluding 'scientific' thinking, but recognising its limitations and potential for misuse.
Keywords: Merleau-Ponty; evidence-based medicine; ontology; philosophy; psychometric measures; truth.