 Vertical vs. horizontal pluralism. Vertical pluralism is inter-level pluralism, the view that there is more than one level of factual description or kind of fact and that each is irreducible, equally fundamental, or ontologically/conceptually autonomous. Horizontal pluralism is intra-level pluralism, the view that there may be incompatible descriptions or facts on the same level of discourse (Lynch 1998). For instance, the plurality of explanatory causes to be chosen from or integrated in biology or physics has been defended as lesson in pluralism (Sober 1999).