"Rosen quotes various passages from De Revolutionibus in which Copernicus uses without distinction, the terms: principle, assumption and hypothesis, for fundamental s: "Furthermore astronomy, that divine rather than human science, which inquires into the loftiest things, is not free from difficulties. Especially with regard to its principles (principia) and assumptions (assumptiones), which the Greek call 'hypotheses' (hypotheses)..." These axioms, in order to be recognized as true, must satisfy two conditions: 1) apparentias salvare (save the appearances): "the results deduced from them must agree with the observed phenomena within satisfactory limits of error."..: 2) aequalitatem tueri [to protect equality]: "They must be consistent with certain preconceptions, called 'axioms of physics,' such as that every celestial motion is circular, every celestial motion is uniform, and so forth.""