Biological naturalism is a theory about, among other things, the relationship between consciousness and body (i.e. brain), and hence an approach to the mind–body problem. It was first proposed by the philosopher John Searle in 1980 and is defined by two main theses: 1) all mental phenomena from pains, tickles, and itches to the most abstruse thoughts are caused by lower-level neurobiological processes in the brain; and 2) mental phenomena are higher-level features of the brain. This entails that the brain has the right causal powers to produce intentionality. However, Searle's biological naturalism does not entail that brains and only brains can cause consciousness. Searle is careful to point out that while it appears to be the case that certain brain functions are sufficient for producing conscious states, our current state of neurobiological knowledge prevents us from concluding that they are necessary for producing consciousness. In his own words: "The fact that brain processes cause consciousness does not imply that only brains can be conscious. The brain is a biological machine, and we might build an artificial machine that was conscious; just as the heart is a machine, and we have built artificial hearts. Because we do not know exactly how the brain does it we are not yet in a position to know how to do it artificially." (Biological Naturalism, 2004) Overview Searle denies Cartesian dualism, the idea that the mind is a separate kind of substance to the body, as this contradicts our entire understanding of physics, and unlike Descartes, he does not bring God into the problem. Indeed, Searle denies any kind of dualism, the traditional alternative to monism, claiming the distinction is a mistake. He rejects the idea that because the mind is not objectively viewable, it does not fall under the rubric of physics. Searle believes that consciousness "is a real part of the real world and it cannot be eliminated in favor of, or reduced to, something else" whether that something else is a neurological state of the brain or a computer program. He contends, for example, that the software known as Deep Blue knows nothing about chess. He also believes that consciousness is both a cause of events in the body and a response to events in the body. On the other hand, Searle doesn't treat consciousness as a ghost in the machine. He treats it, rather, as a state of the brain.