Externalism is a group of positions in the philosophy of mind which argues that the conscious mind is not only the result of what is going on inside the nervous system (or the brain), but also what occurs or exists outside the subject. It is contrasted with internalism which holds that the mind emerges from neural activity alone. Externalism is a belief that the mind is not just the brain or functions of the brain.
There are different versions of externalism based on different beliefs about what the mind is taken to be. Externalism stresses factors external to the nervous system. At one extreme, the mind could possibly depend on external factors. At the opposite extreme, the mind necessarily depends on external factors. The extreme view of externalism argues either that the mind is constituted by or identical with processes partially or totally external to the nervous system.
Another important criterion in externalist theory is to which aspect of the mind is addressed. Some externalists focus on cognitive aspects of the mind – such as Andy Clark and David Chalmers,Shaun Gallagher and many others – while others engage either the phenomenal aspect of the mind or the conscious mind itself. Several philosophers consider the conscious phenomenal content and activity, such as William Lycan, Alex Byrne or Francois Tonneau; Teed Rockwell or Riccardo Manzotti.
A neurobiological theory that relies on externalism for explanation of mental phenomena is called practopoiesis.
The Proto-externalist group includes authors who were not considered as externalist but whose work suggest views similar to current forms of externalism. The first group of protexternalists to consider is the group of neorealists active at the beginning of 1900. In particular, Edwin Holt suggested a view of perception that considered the external world as constitutive of mental content. His rejection of representation paved the way to consider the external object as being somehow directly perceived: “Nothing can represent a thing but that thing itself”. Holt’s words anticipated by almost a century the anti-representationalist slogan by Rodney Brooks: "The world is its best representation".