The problem was famously addressed by René Descartes in the 17th
century, resulting in Cartesian dualism, and by pre-Aristotelian
philosophers, in Avicennian philosophy, and in earlier Asian
traditions. A variety of approaches have been proposed. Most are
either dualist or monist. Dualism maintains a rigid distinction
between the realms of mind and matter. Monism maintains that
there is only one kind of stuff, and that mind and matter are
both aspects of it. Each of these categories itself contains
numerous variants. The two main forms of dualism are substance
dualism, which holds that the mind is formed of a distinct type
of substance not governed by the laws of physics, and property
dualism, which holds that the laws of physics are universally
valid but cannot be used to explain the mind. The three main
forms of monism are physicalism, which holds that the mind
consists of matter organized in a particular way; idealism,
which holds that only thought truly exists and matter is merely
an illusion; and neutral