 Historically, existence monism may have been defended by Parmenides, Melissus, Spinoza, and Bradley, though in each case the claim is  controversial.[9]  Among contemporary philosophers, Horgan and Potrč are probably the leading, and perhaps the only, existence  monists.[10]  Thus Horgan and Potrč (2000: 249; c.f. 2008: 8) advance the following ontological and semantical theses: