Abstract
It is commonly held that our thoughts, beliefs, desires and feelings - the mental phenomena that we instantiate - are constituted by states and processes that occur inside our head. The view known as externalism, however, denies that mental phenomena are internal in this sense. The mind is not purely in the head. Mental phenomena are hybrid entities that straddle both internal state and processes and things occurring in the outside world. The development of externalist conceptions of the mind is one of the most controversial, and arguably one of the most important, developments in the philosop.