Modal fictionalism is a term used in philosophy, and more specifically in modal logic, to describe the position that holds that talk of possible worlds is actually false, though adopting such a discourse may be a useful fiction. A contrast to the position of modal fictionalism would be the position of modal realism, which holds that possible worlds exist and are as real as our world. Modal realism was most famously advanced by the 20th-century thinker David Lewis.