... science is a process that builds continuously upon existing theories—that is, upon existing cumulated knowledge—but continuously revises this knowledge, keeping the possibility open of questioning any aspect of it, including the general rules of thinking that appear to be most certain and beyond question.
It follows that scientific theories are not incommensurable, as some contemporary philosophy of science would have it. Theories can be easily translated into one another, including insufficiencies, approximations, and errors. Copernicus’s discovery that the Earth revolves around the Sun remains true within the frameworks of Newton and Einstein. The discovery is translated and re-expressed in the new language. There may be great differences between Copernicus’s language and the new ones, but the discovery remains recognizable. In fact, Copernicus’s theoretical discovery survives not only as a true fact about nature (the Earth revolves around the Sun) but even as a key conceptual ingredient of the new conceptual systems (there is a “Copernican principle” in Einstein’s cosmology).
Perhaps the most obvious example of what I mean is provided precisely by the Copernican revolution itself, the prototype of scientific revolution and conceptual reorganization. Ptolemy’s Almagest and Copernicus’s De revolutionibus are two of the finest scientific works ever written. In moving from the first to the second, the cosmos is turned upside down. In Ptolemy, there are Heaven and Earth. One category includes all everyday objects and the Earth upon which we walk, the other includes Moon, Sun, stars, and planets. In Copernicus, there is the Sun in one category; Mercury, Venus, the Earth, Mars, Jupiter, and Saturn in a second one; and the Moon, alone, in yet another category. Before, we were still; after, we are on a top spinning along at thirty kilometers per second. Can one even imagine a greater conceptual leap? Can two so very different conceptual systems even talk to each other?
Well, open the two books: Copernicus’s treatise, as observed earlier, is extraordinarily similar to Ptolemy’s; indeed, it seems almost a corrected edition of Ptolemy’s! Same language, mathematics, epicycles, deferents, tables of trigonometric functions, techniques, same general structure, same meticulousness, and same immense, vast vision. The two are impressively similar, and different from anything else written earlier or later. Incommensurability? It is obviously the same research program. If there exist two people who truly understand each other, they are Ptolemy and Copernicus. They could almost be lovers.—The First Scientist: Anaximander and His Legacy, by Carlo Rovelli, 2011