SummaryThe term ‘category mistake’ began to turn up regularly in public discourse in the 1990s as a general term to describe a confusion between different fields of thought with serious practical consequences. But it began its career in philosophy, introduced by Gilbert Ryle in The Concept of Mind in 1949 to attack Cartesian dualism and assert a monistic solution to the so-called mind-body problem. This paper traces the stages by which it came into general usage, arguing that while by the (...) later 1960s it had generally been rejected by philosophers, it was saved from disappearance by its migration into fields such as psychology and theology. From there, it moved into critical theory and then into international relations. Its entry into these latter areas first made plain its potential in political argument. Eventually, multiple meanings of the term came to coexist with one another, with the practical and rhetorical usage supplementing rather than replacing its original philosophical sense. (shrink)