William Isaac Thomas

13 August 1863 – 5 December 1947

William Isaac Thomas was an American sociologist. Working with Polish sociologist Florian Znaniecki, W.I. Thomas developed innovative work on the sociology of migration. Thomas then went on to formulate a fundamental principle of sociology, known as the Thomas theorem. Through his theorem, Thomas contended that, "If men define situations as real, they are real in their consequences" - Wikipedia