Newtonian Absolute Time vs Fluxional Time

In this paper, I will first very briefly recall some features of Newtonian absolute, true, and mathematical time (absolute time, for short) as defined in the Principia. What I will try to do is to explain why Newton needed to resort to the idea of absolute time in his natural philosophy, and why he introduced this concept that –as we know from Einstein’s work– must actually be rejected in contemporary physics. I will then move on to consider the characterization of time employed in the method of fluxions, what I call “fluxional time”. Again, I will underline why Newton introduced this concept in his method of fluxions. He did so about two decades before writing the Principia, in a context that is quite different from the natural philosophy of force, acceleration and gravitation that was top of the agenda for the author of the Principia.