In 1921 Nelson presented what seems to be the first theory of philosophical argumentation, or at least of its negative or destructive part—a theory of philosophical fallacies. That theory says that the peculiar nature of philosophical thinking repeatedly leads people to take ordinary concepts with great philosophical import, such as causality or duty, and replace them with new, made-up ones, whose content is very different from that of the originally available ones. When the new concepts usurp the place of the original ones within a philosophical argument, they invariably produce false results—on all sides of philosophical disputes. Many apparently irresolvable disputes in philosophy are the product of such fallacious concept-swapping.