If the solar eclipse took place, Leibniz noted, that was sufficient proof that he was, in fact, an astronomer, because the probability of someone who is not an astronomer predicting, eyes or no eyes, an eclipse that no other astronomer in the world has predicted is negligible. But if the solar eclipse failed to take place, it was no proof that he was not an astronomer, since it is not only nonastronomers who mispredict eclipses but also astronomers, eyes or no eyes, though of course especially no eyes. The probability of someone who is an astronomer, even a sighted one, mispredicting a solar eclipse is actually quite high, as any induction over past solar eclipse mispredictions will indicate, since astronomers, even the sighted ones, are constantly mispredicting eclipses. “If the eclipse does occur we can deduce that he is actually an astronomer and actually sane, but if the eclipse fails to occur we can deduce nothing at all—not that he is not an astronomer, not that he is a fraud, not that he is not sane: nothing!” Leibniz suddenly realized the one-sidedness of the sanity assessment that would shortly, for it was now almost nine o’clock in the morning, be administered by God in the form of a solar eclipse occurring or failing to occur. If the old man passed the test he was indeed sane, but if he failed the test it was no proof that he was not sane.

He could fail God’s assessment without failing mine, Leibniz wrote.