"Newton then elevates this approximate empirical discovery to the position of a rigorous principle, the principle of inertia, and states that absolutely free bodies hence will cover equal distances in equal times. ...It is the principle of inertia coupled with an understanding of spatial congruence that yields us a definition of congruent stretches of absolute time. ...The principle of inertia, together with the other fundamental principles of mechanics, enables us... to place mechanics on a rigorous mathematical basis, and rational mechanics is the result. ...science, in the case of mechanics, has followed the same course as in geometry. Initially our information is empirical and suffers from all the inaccuracies ...But this empirical information is idealised, then crystallised into axioms, postulates or principles susceptible of direct mathematical treatment. ...If peradventure further experiment were to prove that our mathematical deductions ...were not born out in the world of reality, we should have to modify our initial principles and postulates or else agree that nature is irrational. With mechanics, the necessity of modifying the fundamental principles became imperative when it was recognized that the mass of a body was not the constant magnitude we thought it to be; hence it was experiment that brought about the revolution. On the other hand, in the case of geometry, it was the mathematicians themselves who forsaw the possibility of various non-Euclidean doctrines, prior to any suggestion of this sort being demanded by experiment."