||The idea that some scientific theories may be incommensurable was introduced by Thomas Kuhn and Paul Feyerabend in 1962. In Kuhn's original discussion, the idea of incommensurability included semantic, perceptual and methodological components. By contrast, Feyerabend's discussion of incommensurability restricted it to the semantic sphere. The use of the term 'incommensurability' in the philosophy of science is a borrowing from mathematics, where it implies the absence of a common unit of measurement. Applied to the philosophy of science, it may be taken to mean that there are no shared standards by which competing theories are to be evaluated. In some contexts, it may be taken to mean that the content of competing theories is unable to be directly compared due to semantic variation between the theories.