 To a large extent Boyle accepted these points. He notes explicitly that none of the proofs he was prepared to offer amounted to a demonstration of God’s existence, and indeed he felt that a demonstration was not possible. A demonstration was typically held to proceed from necessarily true premises (often Aristotelian  principles[26])  via a valid argument to a necessarily true conclusion, and part of what was at issue was whether we should be looking for a demonstration of God’s existence, or something less which would nonetheless still be useful in the fight against atheism . “To haue the Science of a thing,” said Pierre du Moulin the elder, “two certainties are required. The one is, that the thing be certaine of it selfe and unchangeable. The second is, that the perswasion which wee haue of it be firme and cleare” (Du Moulin 1624, 162). Gassendi agreed, as did Arnauld and Nicole in the Port Royal Logic (Gassendi 1658, Canon XVI, 144; Arnauld 1662, part IV, ch 8, 323–4, pagination as in the 5th, 1683 edition).