The Philosophy of Mind consists of problems concerning aspects and properties of the human mind. The most important of these problems is that of the relation between mind and body, or, more generally, between mental and physical phenomena. Usually referred to as the "mind-body problem", this has been one of the fundamental problems in Philosophy since Descartes (1596-1650) and his critics introduced it four centuries ago. The mental seems, at first glance, completely different from the physical. Physical properties are public, i.e. equally observable by everyone, but mental properties are not. It can be deduced that someone feels pain by his behaviour, but only that person can feel it directly. Conscious mental events are private in the sense that the subject has privileged access to them that no one has for the physical. Conscious experiences, such as the smell of jasmine, are completely different from the configurations and movements, however complex, of particles, atoms and molecules, or the physical changes of cells and tissues. Despite this, conscious phenomena do not seem to arise out of nothing, but from physical-biological processes in the body, especially from neural processes in the brain. But how can physical-biological systems have states such as thoughts, fears and hopes?