  Internalism in the first instance is a thesis about the basis of either knowledge or justified belief. This first form of internalism holds that a person either does or can have a form of access to the basis for knowledge or justified belief. The key idea is that the person either is or can be aware of this basis. Externalists, by contrast, deny that one always can have this sort of access to the basis for one's knowledge and justified belief. A second form of internalism, connected just to justified belief but probably extendable to knowledge as well, concerns not access but rather what the basis for a justified belief really is. Mentalism is the thesis that what ultimately justifies any belief is some mental state of the epistemic agent holding that belief. Externalism on this dimension, then, would be the view that things other than mental states operate as justifiers. A third form of internalism concerns the very concept of justification, rather than access to or the nature of justifiers. This third form of internalism is the deontological concept of justification, whose main idea is that the concept of epistemic justification is to be analyzed in terms of fulfilling one's intellectual duties or responsibilities. Externalism with respect to the concept of epistemic justification would be the thesis that this concept is to be analyzed in terms other than special duties or responsibilities.