ABSTRACT
Measurement is one of the most distinctive and pervasive features of modern science, but it is not easy to say what measurement actually is. Philosophers commonly define measurement as the correct assignment of numbers to physical variables. There are many difficult philosophical and practical questions about whether a measurement is made correctly and how we can know that it is. various philosophical views surrounding these questions are discussed next; in the final two sections, we highlight concrete questions concerning the practice of measurement in the physical and the social sciences.
