The presentist aims to restrict what exists in time to what exists in time now. Call this the presentist restriction. But if the presentist says that only what exists now, exists, he cannot possibly mean that only what exists at the time of his utterance or thought of the presentist thesis exists. If it is now 5:05 AM GMT on 20 March 2013 anno domini, the presentist thesis is not that only what exists at 5:05 AM GMT on 20 March 2013 anno domini exists. The presentist is not a solipsist of the present moment. He is a metaphysician, not a lunatic. Nor is presentism an infinite family of time-indexed theses, but one thesis about time and existence.
The presentist restriction is not to the time that happens to be present, but to each time: Each time t is such that whatever exists in time exists at t. Formulated so as to avoid the solipsism of the present moment, the formulation must quantify over times. But whatever we quantify over must exist: it must be there to be quantified over. So nonpresent times must exist. But nonpresent times cannot exist if presentism is true and only what is present exists.
Therefore, when formulated so as to evade SPM, presentism entails its own falsity. If true, then false. If false, then False. Ergo, necessarily false.
But 'surely' it cannot be that easy to refute presentism! So I must have gone wrong somewhere. Where exactly?
Over Sunday breakfast, Peter L. suggested that the presentist can make an exception in the case of (nonpresent) times. But then the presentist thesis is drastically weakened. Moreover, no presentist that I know of makes such an exception.
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