Of all philosophical writers on metaphor, Nietzsche probably draws the strongest conclusions from this situation. ''Tropes,'' he writes, ''are not something that can be added or abstracted from language at will—they are its truest nature.'' He argues that there is ''no real knowing apart from metaphor,'' by which he means that we experience reality through metaphors, and our notion of literal meaning simply reflects the ossification of language, as figures of speech lose their vitality. He emphasizes in The Genealogy of Morals how metaphor tends to extend its sway, to bring wider ranges of experience under its wing. He goes so far as to say that ''the drive toward the formation of metaphor is the fundamental human drive.'' For him, literal and figurative meaning are not stable categories, but historical ones determined by their social context.