is true that Marie Curie discovered polonium, but they deny that the event of her discovery exists (because it is a wholly past event). Presentists have been charged with violating the plausible truth-maker principle (that truths require truth-makers) and ontologically 'cheating'. Presentists can respond to this objection either by denying that truths about the past require truth-makers (that is, they can accept the truth-maker principle for some truths, but deny that it applies in full generality, or else reject the truth-maker principle wholesale), or by locating presently existing entities to play the role of truth-makers for truths about the past. See also Appeal to novelty A-series and B-series Arrow of time Centered worlds Endurantism Eternity Growing block universe Perdurantism Problem of future contingents Specious present References External links . . Dowden, Bradley. "Time". Internet Encyclopedia of Philosophy. . . . Describes Presentism and how four dimensionalism contradicts it. Metaphysical theories Philosophy of time Theory of relativity