Descartes is often regarded as the first thinker to emphasize the use of reason to develop the natural sciences. For him the philosophy was a thinking system that embodied all knowledge, and expressed philosophy like a tree, of which Metaphysics is the root, Physics the trunk, and all the other sciences the branches that grow out of this trunk. And he attempted to arrive at a fundamental set of principles that one can know as true without any doubt.
Dualism (the assumption that mental phenomena are, in some respects non-physical, or that the mind and body are distinct) is closely associated with the philosophy of Descartes which holds that the mind is a nonphysical substance. Descartes clearly identified the mind with consciousness and self-awareness and distinguished this from the brain as the seat of intelligence.
So what does this have with psychology today?
Whilst many of us haven’t studied philosophy, we do however, share core philosophical beliefs. These tenets, even if we don't articulate or label them, shape our principles and faith and guide our judgments and actions. For example, a lot of us wouldn’t identify ourselves as dualists if questioned, yet many of us profess beliefs in heaven, in reincarnation, in supernatural spirits, and so forth. These are dualist beliefs. That is, they all assume that the mind and body are different entities - and that one can exist without the other.
In fact, there is growing evidence that humans are natural-born dualists and what's more, that this natural philosophy has important real-life consequences. One piece of recent work by psychological scientist Matthias Forstmann and his colleagues at the University of Cologne, in Germany examined possible link between philosophy and lifestyle, specifically between dualist beliefs and health consciousness.
Here is their reasoning: Since dualists view the body as separate and independent from the mind, shouldn't they tend to see their bodies as mere vessels, or tools? And if so, dualist thinkers would be expected to be less careful with their bodies, more neglectful of their fitness and health.
Their work is reported in a forthcoming issue of the journal Psychological Science, and finds that [laboratory] dualists were less healthy on every measure. They had more reckless attitudes toward health and exercise; they preferred barbecue and dessert cookbooks over organic and vegetarian ones; they ate less nutritional cafeteria meals when given the choice; and they even recalled and described their overall lifestyle as less health-focused. Those considered as physicalist beliefs were the opposite on all these measures.