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Kreeft has received several honors for achievements in philosophical reasoning. They include the following: Woodrow Wilson, Yale-Sterling Fellowship, Newman Alumni Scholarship, Danforth Asian Religions Fellowship, and Weathersfield Homeland Foundation Fellowship.
Kreeft joined the philosophy faculty of the Department of Philosophy of Boston College in 1965. He has debated several academics in issues related to God's existence. Shortly after he began teaching at Boston College he was challenged to a debate on the existence of God between himself and Paul Breines, an atheist and history professor, which was attended by a majority of undergraduate students. Kreeft later used many of the arguments in this debate to create the Handbook of Christian Apologetics with then undergraduate student Ronald K. Tacelli, S.J..
In 1971 Kreeft published an article entitled "Zen In Heidegger's 'Gelassenheit'" in the peer-reviewed journal International Philosophical Quarterly, the philosophy journal published by Kreeft's alma mater, Fordham University. In 1994, he was a signer of the document "Evangelicals and Catholics Together". He also formulated, with R. Tacelli, SJ, "Twenty Arguments for the Existence of God", which he calls a "cumulative case" and that "all twenty taken together, like twined rope, make a very strong case" he states.
A Calvinist, Kreeft regarded the Catholic Church "with the utmost suspicion." A key turning point was when he was asked by a Calvinist professor to investigate the claims of the Catholic Church that it traced itself to the early Church. He said that on his own, he "discovered in the early Church such Catholic elements as the centrality of the Eucharist, the Real Presence, prayers to saints, devotion to Mary, an insistence on visible unity, and apostolic succession." The Church fathers such as Augustine and Jerome were clearly Catholic and not Protestant, he stated.
The "central and deciding" factor for his conversion was "the Church's claim to be the one Church historically founded by Christ." For he applies C. S. Lewis's trilemma—either Jesus is a liar, a lunatic, or the Lord to the Church: "either that this is the most arrogant, blasphemous and wicked claim imaginable, if it is not true, or else that He is just what He claims to be."
On the Bible issue, he refers to the church preaching that forms the basis for writing the Bible and the approval needed from the church to ascertain the contents of the Bible. To this he applied the axiom: "a cause can never be less than its effect. You can't give what you don't have. If the Church has no divine inspiration and no infallibility, no divine authority, then neither can the New Testament."
His conversion took place as he asked God for help, praying that "God would decide for me, for I am good at thinking but bad at acting, like Hamlet." It was then that he says he "seemed to sense" the call of saints and his favorite heroes, to which he assented.
According to Kreeft's personal account, his conversion to Catholicism was influenced by things such as:
the thought of the relatively small number of Calvinists vis-a-vis God's willingness to save many - because if the Bible tells us that God is going to save many, then it seems that he must be intending to do so.
a simple way of understanding God's demands in terms of asking God what he wants us to do, and then doing it
the logic of asking saints to pray for us as we ask friends to pray for us
medieval art and philosophy (Gothic architecture, Thomistic philosophy)
reading St. John of the Cross whose writings he viewed as really "something as massive and positive as a mountain range"
a visit to St. Patrick's Cathedral in New York when he was twelve years old, "feeling like I was in heaven... and wondering why, if Catholics got everything else wrong, as I had been taught, they got beauty so right. How could falsehood and evil be so beautiful?"
"Let's get very, very basic and very, very practical about prayer. The single most important piece of advice I know about prayer is also the simplest: Just do it! The major obstacle in most of our lives to just saying yes to prayer, the most popular and powerful excuse we give for not praying, or not praying more, or not praying regularly, is that we have no time. The only effective answer to that excuse, I find, is a kind of murder. You have to kill something, you have to say no to something else, in order to make time to pray."
"Without qualification, without ifs, ands, or buts, God's word tells us, straight as a left jab, that love is the greatest thing there is (1 Cor 13: 13). Scripture never says God is justice or beauty or righteousness, though he is just and beautiful and righteous. But "God is love" (1 Jn 4:8). Love is God's essence, his whole being. Everything in him is love. Even his justice is love. Paul identifies "the justice of God" in Romans 1:17 with the most unjust event in all history, deicide, the crucifixion, for that was God's great act of love."
"Ideas are more precious than diamonds. The three most precious ideas I have ever discovered all concern the love of God."
"What is God's Answer to Human Suffering? The answer must be someone, not just something. For the problem (suffering) is about someone (God—why does he... why doesn't he ...?) rather than just something. To question God's goodness is not just an intellectual experiment. It is rebellion or tears. It is a little child with tears in its eyes looking up at Daddy and weeping, "Why?" The hurt child needs not so much explanations as reassurances. And that is what we get: the reassurance of the Father in the person of Jesus, 'he who has seen me has seen the Father' (Jn 14:9)."
"Saints are not freaks or exceptions, they are the standard operating model for human beings. Because, as Charles Péguy put it, “life holds only one tragedy, ultimately: not to have been a saint.” In fact, in the biblical sense of the word, all believers are saints. Saints are not the opposite of sinners. There are no opposites of sinners in this world. There are only saved sinners and unsaved sinners. Thus holy does not mean “sinless” but “set-apart:” called out of the world to the destiny of eternal ecstasy with God."
Charisms: Visions, Tongues, Healing, etc. (feat. Dave Nevins) (2013) — catalysts to "two-way" interactive prayer
Jacob's Ladder (2013) — Ten Steps to Truth
Summa Philosophica (2012) — 110 Key Questions in Philosophy
Socrates Meets Hume (2010) - The Father of Philosophy Meets the Father of Modern Skepticism
Between Allah & Jesus: what Christians Can Learn from Muslims (2010)
Socrates Meets Kant (2009) — The Father of Philosophy Meets His Most Influential Modern Child
Because God Is Real : Sixteen Questions, One Answer (2008)
The Philosophy of Jesus (2007) — On the wisdom of Jesus
Socrates Meets Descartes (2007) - The Father of Philosophy Analyzes the Father of Modern Philosophy's Discourse on Method
The Sea Within (2006)
The Philosophy of Tolkien: The Worldview Behind "The Lord of the Rings" (2005)
Socrates Meets Sartre : Father Of Philosophy Meets The Founder of Existentialism (2005) — Socrates and Jean-Paul Sartre
You Can Understand the Bible (2005) - a combination of his previous books You Can Understand the Old Testament: A Book-by-Book Guide for Catholics (1990) and Reading and Praying the New Testament: A Book-by-Book Guide for Catholics (1992)
Socratic Logic (2005) — A textbook on classical logic.
The God Who Loves You (2004)
Socrates Meets Marx (2003) — Socratic dialogue between Socrates and Karl Marx
Socrates Meets Machiavelli (2003) — Socratic dialogue between Socrates and Machiavelli
Philosophy 101 by Socrates (2002) — An introduction to philosophy via Plato's Apology
How to Win the Culture War (2002)
Three Approaches to Abortion (2002)
How to Win the Culture War: A Christian Battle Plan for a Society in Crisis (2002)
Socrates Meets Jesus (1987/2002)— Socratic dialogue with students of Harvard University's Divinity School
Catholic Christianity (2001)
Prayer for Beginners (2000)
Refutation of Moral Relativism — Dialogues between a relativist and absolutist (1999)
The Snakebite Letters Devious Secrets for Subverting Society (1998)
The Journey A Spiritual Roadmap For Modern Pilgrims (1996)
Ecumenical Jihad: Ecumenism and the Culture Wars (1996)
Angels (and Demons): What Do We Really Know About Them? (1995)
Shadow-Lands of C.S. Lewis : The Man Behind the Movie (1994)
C. S. Lewis for the Third Millennium (1994) — Six essays on Lewis' Abolition of Man
Handbook of Christian Apologetics (with Ronald K. Tacelli) (1994)
Christianity for Modern Pagans: Pascal's Pensees (1993)
Shorter Summa (1993) — Shorter version of Kreeft's Summa of the Summa
Back to Virtue (1992)
Three Philosophies of Life (1990) - Ecclesiastes (life as vanity), Job (life as suffering), Song of Songs (life as love)
Summa of the Summa (1990) — Summa Theologica edited and explained for beginners
Making Choices: Practical Wisdom for Everyday Moral Decisions (1990)
Everything You Ever Wanted To Know About Heaven... But Never Dreamed of Asking (1990)
Heaven, the Heart's Deepest Longing (1989)
Fundamentals of the Faith, Essays in Christian Apologetics (1988)
Making Sense Out of Suffering (1986)
Yes or No? (1984) — Straight Answers to Tough Questions about Christianity
The Best Things in Life: (1984) — Twelve Socratic dialogues on modern life
The Unaborted Socrates (1983) — Socratic dialogue on abortion
Between Heaven and Hell: (1982) — A Dialog with John F. Kennedy, C. S. Lewis, and Aldous Huxley
Love Is Stronger Than Death (1979) — On the meaning of death and life