Professor John F. X. Knasas writes,
John F. X. Knasas, “Fides et Ratio and the Metaphysical Basis of Aquinas’ Natural Law,” Notre Dame Center for Ethics and Culture, 2002, conference.
No doubt should exist that Fides et Ratio is referring to Aquinas’ central metaphysical notion of actus essendi.
In discussing the needs of systematic theology, Fides et Ratio mentions the requirement of a “philosophy of being based upon the act of being.” (1) Affixed to this remark is note 115 that references John Paul’s Angelicum address on the occasion of the centenary of Aeterni Patris. A read of that address removes all doubt that the phrase “act of being” is a reference to Aquinas’ notion of “actus essendi .”
(1) Fides et Ratio, paragraph 97: “If the intellectus fidei wishes to integrate all the wealth of the theological tradition, it must turn to the philosophy of being, which should be able to propose anew the problem of being—and this in harmony with the demands and insights of the entire philosophical tradition, including philosophy of more recent times, without lapsing into sterile repetition of antiquated formulas. Set within the Christian metaphysical tradition, the philosophy of being is a dynamic philosophy which views reality in its ontological, causal and communicative structures. It is strong and enduring because it is based upon the very act of being itself, which allows a full and comprehensive openness to reality as a whole, surpassing every limit in order to reach the One who brings all things to fulfillment.”