Definition of "assertor"

When Wittgenstein says that he cannot contradict the assertor of a Last Judgement, he uses (repeatedly) the first person singular. There is no argument that the impossibility of his contradicting the man is a result of his not himself being a religious man, or not being a participant in any religious life, the result, that is, of some condition such that, if anyone were in that condition, he also would not be able to contradict the assertor. He mentions the case of an atheist who does contradict the assertor, and asks whether the atheist means the same by a Last Judgement as does the assertor, but replies that the criterion for meaning the same isn't clear.

2017 Mario von der Ruhr, et al: Religion and Wittgenstein's Legacy;

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1659, J[ohn] M[ilton], “To the Parlament of the Commonwealth of England with the Dominions therof”, in Considerations Touching the Likeliest Means to Remove Hirelings out of the Church. […], London: […] T[homas] N[ewcombe] for L[ivewell] Chapman […]