Philosophical theories of mental content include internalism, externalism, representationalism and intentionality. Phenomenal externalism extends the externalist view to phenomenal content. In practice, the line between internalism and externalism can be incredibly fuzzy. Process reliabilism is a form of epistemic externalism. The question then arises of the possibility of reconciling externalism with holism. Whitehead's process ontology is a form of externalism since it endorses a neutral ontology. He defends a position he himself dubbed "radical externalism" perhaps because of its ontological consequences. Thomas Kuhn is a notable proponent of historiographical externalism. Semantic externalism comes in two varieties, depending on whether meaning is construed cognitively or linguistically. This is the essential thesis of semantic externalism. The traditional discussion on externalism was centered around the semantic aspect of mental content. Semantic externalism is the first form of externalism which was dubbed so. Another attempt to use externalism to refute skepticism is done by Brueckner and Warfield. This is often referred to as the account from externalism or ultra-externalism. This is by no means the only meaning of externalism now.