Counterfactual Heliocentrism.—Suppose someone searching in a neglected archive comes across a manuscript by an astronomer that lays out the Copernican heliocentric theory of cosmology. Further suppose that this predates Copernicus, and suppose that subsequent research reveals that the author in question had access to astronomical observations of at least the level of sophistication of those to which Copernicus had access, so his conclusions are as well-founded as those of Copernicus. Any late medieval astronomer could have had copies of Ptolemy’s Almagest and the Alphonsine Tables, both of which Copernicus relied upon, and Copernicus had no decisively new observational technique or technologies. And seeking to soften the blow of his conclusions, Copernicus, in the best medieval tradition, deferred to an ancient authority: Aristarchus of Samos, none of whose works survive, but Archimedes in The Sand Reckoner records Aristarchus’ heliocentrism. Any medieval astronomer could have had this reference too. Now further suppose that our fictional astronomer died in obscurity, and no one looked at his manuscript until its discovery in the 21st century. We cannot know that there is no manuscript like this. Copernicus did not have especially good astronomical data, what he had was what others at the time had, and his innovations were primarily theoretical. Others could have reached the same conclusions. To what degree would we need to re-write the history of astronomy and of modern science in the light of such a discovery? If we count Copernicus as the beginning of the scientific revolution, should we shift our identification of the advent of modern science to this earlier figure? What is the value, and what is the historical status, of a scientific discovery that influences no one at the time, and no one in subsequent history until it is rediscovered at a time when it is a mere curiosity? Science has many instances of anticipations, more or less explicit, and of simultaneous discovery, so this is question that recurs to us with some regularity. In this fictional scenario is the heliocentric anticipation the origin of anything? Or in its isolation, its position outside customary frameworks of influence, is to not rather a dead end?