"Kuhn used the phrase “normal science” for scientific work that occurs within the framework provided by a paradigm. A key feature of normal science is that it is well organized. Scientists doing normal science tend to agree on which problems are important, on how to approach these problems, and on how to assess possible solutions. … He argued that it is false that science exhibits a permanent openness to the testing of fundamental ideas. Not only that, but science would be worse off if it had the kind of openness that philosophers have treasured. … For Kuhn, there are two distinct kinds of scientific change: change within normal science, and revolutionary science. (These are bridged by “crisis science,” a period of unstable stasis.) These two kinds of change have very different epistemological features; when we try to apply concepts such as justification, rationality, and progress to science, according to Kuhn we find that normal and revolutionary science have to be described very differently. Within normal science, there are clear and agreed-upon standards for the justification of arguments; within revolutionary science there are not. Within normal science there is clear progress; within revolutionary science it is very hard to tell (and it is hard to even interpret the question)."