Copernicus’ Rhetorics: Observational Tests Against the Movement of the Earth and the Theory of Impetus

Abstract

Copernicus’ arguments in favour of the movement of the Earth were often said to be rhetorical. The fact that the nature of this argumentation is more rhetorical than demonstrative is supported by Copernicus’ formulation of one of the observational tests against the movement of the Earth. The argument, according to which projectiles ejected straight up into the air should – in view of the hypothesis of the rotation of the Earth – fall behind the place from which they were ejected, is for Buridan magis demonstrativa apparentia against the movement of the Earth. And it is exactly this argument that Copernicus presented in a very weak form. According to the author of the article, this weak formulation of the argument against the movement of the Earth is a result of Copernicus’ acceptance of certain basic postulates of the theory of impetus, which was the key factor why Buridan in the above mentioned case concluded that the Earth is at rest. Since Copernicus wanted to avoid this conclusion, he had to formulate the argument in a weak form.