In The Structure of Scientific Revolutions periods of normal science and revolutionary science are clearly distinguished. In particular paradigms and their theories are not questioned and not changed in normal science whereas they are questioned and are changed in revolutionary science.  Thus a revolution is, by definition revisionary, and normal science is not (as regards paradigms). Furthermore, normal science does not suffer from the conceptual discontinuities that lead to incommensurability whereas revolutions do. This gives the impression, confirmed by Kuhn’s examples, that revolutions are particularly significant and reasonably rare episodes in the history of science.