One open question regarding the nature of the mind is the mind–body problem, which investigates the relation of the mind to the physical brain and nervous system. Pre-scientific viewpoints included dualism and idealism, which considered the mind somehow non-physical. Modern views center around physicalism and functionalism, which hold that the mind is roughly identical with the brain or reducible to physical phenomena such as neuronal activity. Another question concerns which types of beings are capable of having minds. For example, whether mind is exclusive to humans, possessed also by some or all animals, by all living things, whether it is a strictly definable characteristic at all, or whether mind can also be a property of some types of human-made machines.
Whatever its nature, it is generally agreed that mind is that which enables a being to have subjective awareness and intentionality towards their environment, to perceive and respond to stimuli with some kind of agency, and to have consciousness, including thinking and feeling.
The concept of mind is understood in many different ways by many different cultural and religious traditions. Some see mind as a property exclusive to humans whereas others ascribe properties of mind to non-living entities (e.g. panpsychism and animism), to animals and to deities. Some of the earliest recorded speculations linked mind (sometimes described as identical with soul or spirit) to theories concerning both life after death, and cosmological and natural order, for example in the doctrines of Zoroaster, the Buddha, Plato, Aristotle, and other ancient Greek, Indian and, later, Islamic and medieval European philosophers.
Important philosophers of mind include Plato, Descartes, Leibniz, Locke, Berkeley, Hume, Kant, Hegel, Schopenhauer, Searle, Dennett, Fodor, Nagel, and Chalmers. Psychologists such as Freud and James, and computer scientists such as Turing and Putnam developed influential theories about the nature of the mind. The possibility of non-human minds is explored in the field of artificial intelligence, which works closely in relation with cybernetics and information theory to understand the ways in which information processing by nonbiological machines is comparable or different to mental phenomena in the human mind.
The mind is also portrayed as the stream of consciousness where sense impressions and mental phenomena are constantly changing