Some economists define full employment somewhat differently, as the unemployment rate at which inflation does not continuously increase. Advocacy of avoiding accelerating inflation is based on a theory centered on the concept of the Non-Accelerating Inflation Rate of Unemployment (NAIRU), and those who hold it usually mean NAIRU when speaking of full employment. The NAIRU has also been described by Milton Friedman, among others, as the "natural" rate of unemployment. Such views tend to emphasize sustainability, noting that a government cannot sustain unemployment rates below the NAIRU forever: inflation will continue to grow so long as unemployment lies below the NAIRU.