Some philosophers have also objected to Jackson's first premise by arguing that Mary could not know all the physical facts about color vision prior to leaving the room. Owen Flanagan argues that Jackson's thought experiment "is easy to defeat". He grants that "Mary knows everything about color vision that can be expressed in the vocabularies of a complete physics, chemistry, and neuroscience," and then distinguishes between "metaphysical physicalism" and "linguistic physicalism": Metaphysical physicalism simply asserts that what there is, and all there is, is physical stuff and its relations. Linguistic physicalism is the thesis that everything physical can be expressed or captured in the languages of the basic sciences…Linguistic physicalism is stronger than metaphysical physicalism and less plausible. Flanagan argues that, while Mary has all the facts that are expressible in "explicitly physical language", she can only be said to have all the facts if one accepts linguistic physicalism. A metaphysical physicalist can simply deny linguistic physicalism and hold that Mary's learning what seeing red is like, though it cannot be expressed in language, is nevertheless a fact about the physical world, since the physical is all that exists. Similarly to Flanagan, Torin Alter contends that Jackson conflates physical facts with "discursively learnable" facts, without justification: ...some facts about conscious experiences of various kinds cannot be learned through purely discursive means. This, however, does not yet license any further conclusions about the nature of the experiences that these discursively unlearnable facts are about. In particular, it does not entitle us to infer that these experiences are not physical events. Nida-Rümelin argues in response to such views that it is "hard to understand what it is for a property or a fact to be physical once we drop the assumption that physical properties and physical facts are just those properties and facts that can be expressed in physical terminology."