Presentism's intuitive appeal rests on taking ordinary tensed language at face value: when someone says a historical figure lived and died, or that an event will happen next week, the natural reading is that the dead figure genuinely does not exist any longer and the future event genuinely does not exist yet, not merely that both are located at times other than the present, as eternalism would have it. On this view, the passage of time is not an illusion generated by an observer's limited perspective on an already complete four-dimensional block, but a real, ongoing process in which new moments of reality come into being and old ones genuinely cease to be, one after another, so that the world is metaphysically growing, or at least metaphysically changing, rather than sitting complete and static.
The position's most serious difficulty is reconciling this picture with special relativity, which denies that there is any single, physically privileged present moment shared by all observers everywhere, since what counts as simultaneous with here and now differs depending on an observer's velocity; presentists have responded in several ways, some restricting the theory's scope to a preferred reference frame, others arguing relativity describes only how time is measured rather than settling the deeper metaphysical question of what is ultimately real, though neither response has fully persuaded critics who take relativity's verdict on simultaneity at face value.