In general relativity, Newton's inertial frames are no longer privileged. In quantum mechanics, Paul Dirac argued that physical models were not there to provide semantic constructs allowing us to "understand" microscopic physics in language comparable to that we use on the familiar scale of everyday objects. His attitude, adopted by many theoretical physicists, is that a good model is judged by our capacity to use it to calculate physical quantities that can be tested experimentally. Dirac's view is close to what Bas van Fraassen calls constructive empiricism.