Externalism is a group of positions in the philosophy of mind which hold that the mind is not only the result of what is going on inside the nervous system (or the brain) but also of what either occurs or exists outside the subject. It is often contrasted with internalism which holds that the mind emerges from neural activity alone. Externalism articulates the belief that the mind is not just the brain or what the brain does.There are different versions of externalism based both on the strength of the relation, and on what the mind is taken to be. Externalism stresses the importance of factors external to the nervous system. At one extreme, the mind could possibly depend on external factors. At the opposite extreme, the mind depends necessarily on external factors. The most extreme form of externalism maintains that the mind is either constituted by or identical with physical processes partially or totally external to the nervous system.Another important criterion is which aspect of the mind is addressed. Some externalists focus on purely cognitive aspects of the mind – such as Andy Clark and David Chalmers, Shaun Gallagher and many others – while some tackle either the phenomenal aspect of the mind or the conscious mind itself. A few consider only the phenomenal content, such as William Lycan, Alex Byrne or Francois Tonneau; while others also argue the role of the mind as a vehicle of [mental phenomenal[clarification needed] activity, such as Teed Rockwell or Riccardo Manzotti.One last important differentiating factor is whether what is external to the mind is the content or the vehicle of the mind.