Authors Peter Kreeft and Ronald Tacelli, in their Handbook of Christian Apologetics, provide helpful distinctions and definitions of faith and reason. To begin with, we need to distinguish the objects of faith and reason from the acts of faith and reason. For faith, the object is all things believed. For all orthodox Christians that would include the Bible. Catholics and some Protestant denominations would also include creeds as objects of faith. The ultimate object of faith is God, but the truth propositions contained in the Bible and the creeds are proximate objects of faith that serve as the structure for faith in God. The act of faith, according to the authors, is subdivided by ascending hierarchy into emotional faith, intellectual faith, volitional faith, and heart faith. Emotional faith is little more than feeling confident in a person. Intellectual faith is that which is “formulated in propositions and summarized in creeds.” Volitional faith is an act of the will that manifests itself in behavior. Finally, heart faith, originating from the “absolute center of the soul,” is most interior and substantial act of faith. Scripturally, the “heart of man is his very person; his psychological core. The conscious awareness each of us has that makes us persons and the spiritual dimension of responsiveness or unresponsiveness to God are both expressed by the word ‘heart.’” Thus, when the Bible speaks of Pharaoh’s heart being hardened, it is referring to the condition of the core of his being as regards his lack of faith toward God.
Likewise, we distinguish between the object and act of reason. Kreeft and Tacelli observe that the object of reason, or all that reason can know, includes all truths that can be understood, discovered, or proved by naked reason apart from divine revelation. An example of an object of pure reason would be the molecular composition of water. Another example would be a historical truth such as “Jesus died on a cross.” Assuming objectivity in history, no divine revelation is needed for reason to know that a man named Jesus died on a Roman cross approximately two thousand years ago. If, however, we modify the phrase to read “Jesus Christ died on a cross,” we have added an element of faith to the proposition. The addition of “Christ” necessitates faith in the divine revelation of Scripture for reason itself tells us nothing about the redemptive identity of the historical Jesus. Furthermore, if we added the words “Jesus Christ died on the cross for my sins,” we have once again added an element not discoverable by reason alone. Kreeft and Tacelli provide a good example of how objects of reason and revelation relate. Reason alone can understand, discover, and prove the Pythagorean theorem. Reason alone can also argue for the immortality of the soul. But immortality is also an object of faith. On the other hand, naked reason could never discover that God is a Trinity; that is exclusively an object of faith. The act of reason, for our purposes, operates similar to the objects of reason. As Kreeft and Tacelli point out, the objects of reason, or all that reason can know, correspond to the three acts of the intellect known as understanding, discovering, and proving.
Christian apologetics is impossible without some relation of faith to reason. If there is no way to reasonably communicate the truths of the Christian faith to others, then apologetics is a useless enterprise. Granted, not all apologists agree as to what that relation is, but there must be something common between the two in order to communicate objects of faith. Philosopher J.P. Moreland, debunks the myth that faith is “a blind act of will, a decision to believe something that is either independent of reason or that is a simple choice to believe while ignoring the paltry lack of evidence for what is believed.” He responds to that distorted, but unfortunately popular view by defining faith as “a power or skill to act in accordance with the nature of the kingdom of God, a trust in what we have reason to believe is true. Understood in this way, we see that faith is built on reason.” J. Budziszewski, professor of government and philosophy at the University of Texas, states very simply that faith is “a disposition of reason toward revealed truth.” As these apologists define it, faith and reason, though distinct, are inter-related in a way that makes it possible to give a rational defense of objects of faith.
Kreeft and Tacelli observe that “there are always five possible answers to the question of the relation between any two classes or sets of things.” That being the case, there are five ways in which faith and reason can logically be related. Those five ways can be termed rationalism, fideism, identity, dualism, and partial overlapping.
Identity is the view that whatever can be known by reason can also be known by faith, and vice versa. While that is a logical possibility, the authors note no adherents to the position and it will not be explored here.
Rationalism holds that faith is a subclass of reason. In other words, everything that can be discovered by faith can also be discovered by reason, but not the other way around.
Fideism is the polar opposite of rationalism. Christian apologist Norman Geisler writes that “religious fideism argues matters of faith and religious belief are not supported by reason. Religion is a matter of faith and cannot be argued by reason. One must simply believe.”
Dualism is the “separation of church and state” position. Dualism divorces faith and reason by “(a) reducing reason to scientific, mathematical and empirical reasoning, and (b) reducing faith to a personal, subjective attitude.” Dualism makes religion a “private matter” and, if followed consistently, effectively negates apologetics.
Finally, partial overlapping understands that both faith and reason are avenues to truth, both in their own order. Saints Augustine and Aquinas, the main focus of a latter section of this paper, would both fit in this broad category. What distinguishes Augustine and Aquinas, however, is the specific roles that faith and reason play both prior to and after conversion. The overlap position recognizes that there are truths of faith that are not discoverable by reason, that there are truths of reason not discoverable by faith, and that there are truths that can be known by both faith and reason. The position one takes on the amount and type of overlap will largely determine the approach that one takes to Christian apologetics.