Man is, ergo God must be.…” This concise formulation expresses succinctly the classical mode of attaining natural knowledge of God. Beginning with the mediate phenomenon of the world, Thomas Aquinas was able to postulate the existence of God. Of the various arguments Aquinas used to support his thesis, the best known is the cosmological argument, which led him to the affirmation of an ens necessarium. Simply stated, what Thomas argued was: “Something exists now; therefore something, by necessity, must always have existed.” To substantiate this assertion, the reasoning went that whatever is must either be self-created, created by another, or self-existent. To be self-created, a being must antedate itself, which is absurd. To be created by another presupposes the prior existence of another, which when reasoned backward in time must not become an infinite regress of contingent beings; ergo something must be self-existent. (That is, it must have aseity and its sufficient reason within itself). Arguing further, the Thomist position concluded that neither man nor the world could be conceived as being self-existent, for both clearly demonstrate contingency. Therefore there must be something transcendent and self-existent, who is God.

The cosmological method of Aquinas is not without important points of contact with the ontological method of Augustine and Anselm. Although the latter theologians postulate a more immediate knowledge of God via introspection and reasoning from man’s awareness of his finitude and dependent existence, they like Aquinas start from the existence of man in their reasoning to the existence of God.

The same point of departure is seen in the famous Cartesian formulation, Cogito ergo sum. Descartes’s laborious ...

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