 Prominent in the Quaestiones and Impiété, rational theology tended to recede in importance in subsequent works. Although in the Quaestiones, Mersenne had hinted at another work (“perfectum opus”) to come, it was never written. After 1624 he became more reluctant to consider proofs of God’s existence, hinting in his correspondence with Ruarus that it might not be possible to give a truly demonstrative one, however sensible and approved by everyone was the truth of God’s existence. His doubts were now on a par with the ones he came to entertain regarding demonstrations in physical matters. In his Questions théologiques, he wrote in a somewhat autobiographical tone, that everyone could see for themselves that: