Try this foursome on for size:
1) Memory is a source of knowledge.
2) Whatever is known, exists.
3) Memory includes memory of wholly past individuals and events.
4) Whatever exists, is temporally present.
The limbs of the tetrad are collectively inconsistent: they cannot all be true. To appreciate the logical inconsistency, note that 'exists' in (2) and in (4) have exactly the same sense, and that this is not the present-tensed sense. It is the tense-neutral and time-independent sense. Something that exists in this sense simply exists: it is one of the things listed in the ontological inventory. Hence talk in the literature of existence simpliciter. In both of its occurrences above, 'exists' means: existence simpliciter.
The limbs are individually plausible. But they are not equally plausible. (4) is the least plausible, and thus the most rejectable, i.e., the most rejection-worthy. Rejecting it, we arrive at an argument against presentism given that (4) is a version of presentism, which it is.
1*) Some of what is remembered is known.
2*) All that is known, exists.
Therefore
2.5) Some of what is remembered exists.
3*) All of what is remembered is wholly past.
Therefore
3.5) Some of what exists is wholly past.
Therefore
~4*) It is not the case that whatever exists, is temporally present. (Presentism is false.)
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