A mental event is any event that happens within the mind of a conscious individual. Examples include thoughts, feelings, decisions, dreams, and realizations.
Some believe that mental events are not limited to human thought but can be associated with animals and artificial intelligence as well. Whether mental events are identical to complex physical events, or whether such an identity even makes sense, is central to the mind-body problem.
Some state that the mental and the physical are the very same property which cause any event(s). This view is known as substance monism. An opposing view is substance dualism, which claims that the mental and physical are fundamentally different and can exist independently. A third approach is Donald Davidson's anomalous monism. The Philosophy of Action states that every action is caused by prior thoughts or feelings, and understanding those mental events would in turn explain behavior.
Physicalism, a form of substance monism, states that everything that exists is either physical or depends on that which is physical. The existence of mental events has been used by philosophers as an argument against physicalism. For example, in his 1974 paper What Is it Like to Be a Bat?, Thomas Nagel argues that physicalist theories of mind cannot explain an organism's subjective experience because they cannot account for its mental events.