Johannes Kater (better known under his Latinized name Caterus) was probably born in Haarlem, around 1590. He enrolled at Leuven (Louvain) in 1620 to study theology. He returned to Holland as a secular priest, reporting himself as such (conforming to regulations) to the Amsterdam magistrate in January 1629. In 1632 he was elected to the Haarlem Chapter on condition of obtaining a doctorate in theology. Accordingly, he returned to Louvain in 1634 and obtained degrees in law and theology. In 1638 he became “archpriest” (some sort of dean) of Alkmaar to supervise all pastoral activities in the northern part of the Province of Holland. He was praised for his learning and piety as well as his zeal on behalf of the Catholic religion, which brought him several times in conflict with the civil authorities. Probably at the suggestion of two Haarlem priests, Joan Albert Bannius (1597–1644) and Augustinus Alstenius Bloemaert (ca.1585–1659), two friends of Descartes, who were also members of the Haarlem Chapter, Caterus became the author of the First Objections (see AT III 267, CSMK 164). There is no evidence that at that point Descartes knew Caterus personally, although there is nothing to exclude that possibility either. In any case, Descartes probably knew him somewhat later, because after 1642 he lived almost permanently at Egmond, which is within walking distance (eight kilometers) of Alkmaar.

In the First Objections, Caterus concentrates on Descartes’ proofs of the existence of God, starting with the cosmological argument and the attendant notion of objective being (see being, formal versus objective). According to Caterus, objective being is the thing insofar as it is thought or perceived, not a reality caused by that thing – an “extrinsic denomination that adds nothing to the thing itself” (AT VII 92, CSM II 66–67). As a result, the causal principle does not apply. As for the second cosmological argument for God's existence, which proceeds from the existence of the meditator who possesses the idea of God, Caterus agrees that if a thing is the cause of itself in the positive sense of the word, that is, if it is truly and fully the cause of itself, it would necessarily give itself all the perfections of which it has an idea.