To know that we know what we know, and to know that we do not know what we do not know, that is true knowledge.
Copernicus
The Copernican vision of an earth in motion was not without its rudimentary precedents, as Copernicus himself recounts: "For a long time then, I reflected on this confusion in the astronomical traditions concerning the derivation of the motions of the universe's spheres. I began to be annoyed that the movements of the world machine, created for our sake by the best and most systematic Artisan of all, were not understood with greater certainty by the philosophers, who otherwise examined so precisely the most insignificant trifles of this world. For this reason I undertook the task of rereading the works of all the philosophers which I could obtain to learn whether anyone had ever proposed other motions of the universe's spheres than those expounded by the teachers of astronomy in the schools. And in fact I found in Cicero that Hicetas supposed the earth to move. Later I also discovered in Plutarch that certain others were of this opinion. . . . Therefore, having obtained the opportunity from these sources, I too began to consider the mobility of the earth."
