神の存在証明
In 1971, Kreeft published an article titled "Zen In Heidegger's 'Gelassenheit'" in the peer-reviewed journal "International Philosophical Quarterly", of Fordham University. In 1994, he was an endorser of the document "Evangelicals and Catholics Together". He also formulated, with R. Tacelli, "Twenty Arguments for the Existence of God".