Instrumentalism is one of a multitude of modern schools of thought created by scientists and philosophers throughout the 20th century. The name refers to the fundamental instrumentalist premise that theories are tools in the logical form of means-end relation, rather than true descriptions of nature itself. Its premises and practices were most clearly and persuasively stated by two philosophers, John Dewey (1859-1952) and Karl Popper (1902-1994). Independently, they defined the school quite similarly, but their judgments of its premises were irreconcilable.