The Gospel Coalition

 

Logic

Vern Poythress | Review by: Steven B. Cowan



Vern Sheridan Poythress. Logic: A God-Centered Approach to the Foundation of Western Thought. Wheaton, IL: Crossway, 2013. 708 pp. $45.00.

The relationship between God and logic has long concerned theologians and philosophers, yet few books have been wholly dedicated to exploring it. With Logic: A God-Centered Approach to the Foundation of Western Thought, veteran theologian and Bible scholar Vern Poythress has sought to rectify that situation. He has provided the Christian community with a resource designed to be a detailed and seminal study of logic and its relationship to the triune God of Scripture.

Logic is divided into four major parts. Part 1 presents “Elementary Logic.” Poythress begins by arguing we need a “distinctively Christian approach to logic” (25), one that avoids the modern way of autonomy and listens “submissively to the instruction of Jesus Christ” (35). He contends biblical instruction is necessary to “reform” logic. After explaining the differences between formal/informal logic and deductive/inductive logic, Poythress spends the next ten chapters examining the relationship of God to logic. This is the heart of the book, and it provides implications and results that are applied throughout. For Poythress, the bottom line is that the existence and validity of logical principles depend on a personal, triune God. Because God is sovereign and absolute, this must be the case. This doesn’t mean logic is arbitrary or contingent, however. Instead, it is “in fact an aspect of [God’s] character, because it expresses the consistency of God and the faithfulness of God” (63). Logic actually reveals God’s character. For example, because the logical validity of an argument form holds for all times and places, logical validity reveals God’s eternality and omnipresence.

Part 2 deals with propositional logic. Here, in addition to introducing truth-functional symbols, truth tables, and the like, Poythress continues the theme of God’s sovereignty in logic. “As extensions of language,” he remarks, “these symbols depend on the theistic foundations for language” (240). In Part 3, “Enriching Logic,” Poythress discusses predicate logic, along with some other aspects not normally included in introductory logic texts, such as non-Euclidean geometry, models, and modal logic. Finally, Part 4 gives the reader several appendices and examples for claims made in earlier parts of the book. Included here is a helpful critique of Kantian subjectivism, showing that it is self-defeating. Poythress also includes a generally helpful and insightful treatment of the role of logic in philosophy and how it often leads to the exaltation of human autonomy.

For scholars and teachers who use and/or teach logic, this book is a valuable supplemental resource. It will help them think through the theological presuppositions and implications of logic, as well as hone their knowledge of logical principles. I also strongly commend Poythress for his heartfelt desire to honor, praise, and worship the divine Logos revealed in logic, the one who makes the study and use of logic possible. This aspect of the book is greatly refreshing.

Some Liabilities

That said, however, the book suffers from several liabilities. First, despite how the book is touted on its back cover, it is not really an introductory text. Many chapters go beyond what an introductory student needs to know, some even well beyond what he or she would be able to understand (especially parts 3 and 4).

Second, the book’s unique feature—the relationship of God to logic—turns out to be its weakest. I found much of Poythress’s discussion on this theme to be confusing and frustrating. For one thing, as indicated above, he argues for a uniquely Christian view of logic. I understand this to mean there are uniquely Christian reasons as to why logic’s principles are valid, not that there’s a uniquely Christian logic itself. This is confirmed when Poythress makes a distinction between “logic as it really is” and our “flawed use” of it (59). However, there are places where his choice of words may wrongly suggest a uniquely Christian logic. For example, while answering the question, “What difference does God make in arguments and logic?,” Poythress writes, “But unbelievers are not persuaded by this evidence [for the truth of the gospel]. They are blind to it. At some crucial points they do not accept the arguments, no matter how convincing these arguments may be in their own right” (46). In an earlier chapter, he writes, “People could present arguments back and forth, arguing for or against the proposition that human beings are naturally good. . . . The dispositions of our hearts, whether toward sin or toward righteousness, affect our evaluations” (39). For these reasons, Poythress contends people need the regenerating work of the Holy Spirit to “reform logic.”

I agree people need the Spirit’s help in evaluating the evidence for Christianity, but none of this has to do with logic per se, and Poythress’s suggestion it does may prompt misunderstanding. After all, the Spirit’s regenerating work doesn’t alter the validity of modus ponens. The Spirit cannot make an invalid argument valid or vice-versa. Certainly, people without the Spirit (like those with the Spirit) can misapply logical principles, ignore evidence, and believe propositions that are false and/or irrational. But none of this means unbelievers have a different logic than Christians or even that their logic needs reforming. Their logic may be perfectly fine; it is something else that needs reforming. 

Third, Poythress’s discussion regarding the dependence of logic on God is perplexing. He writes, “The inner loyalty and love of [the trinitarian] God also explains why logic expresses necessary truth. The Father necessarily loves the Son through the Spirit” (89). Also, he states: “Mutual love implies harmony among the persons of the Trinity. Harmony in turn implies consistency. Logic, we have said, is God’s self-consistency. Thus, love implies logic” (89). I confess the implications Poythress sees here are obscure to me. How and why does the inner love and loyalty of God explain the necessary truth of logic? And doesn’t the idea that the Father necessarily loves the Son already (logically) presuppose the existence of necessary truth? And what if, per impossibile, the Father did not love the Son (necessarily or otherwise)? Why would that have any effect on the necessity of logic? Here, I am at a loss.

Last, I’m troubled by Poythress’s discussion on the coherence of the doctrine of the Trinity. Early in the book he suggests that one who objects to the Trinity’s coherence and other Christian doctrines “contradicts the Christian view that says God is the standard for logic” (112). Later in an appendix he responds more directly to those who challenge the Trinity (e.g., Jehovah’s Witnesses): “We rely on our knowledge of the Trinity to arrive at a form of logic that prevents people from attacking the Trinity” (700). Admitting this is circular, he asserts, “Circularity expresses our status as dependent on God. . . . Circular reasoning is licit when it is validly dependent on the archetypal knowledge of the Father and the Son. It is illicit when it sets up idolatrous substitutes” (700). 

This, I’m afraid, is what presuppositional apologetics comes to. Poythress’s defense of the coherence of the Trinity is analogous to a man who shoots an arrow and then draws a bulls-eye around the spot the arrow hits, claiming he hit the target all along. We have no right to claim the Trinity is true, demanding non-Christians embrace it on pain of damnation, if our only defense is that it measures up to a “form of logic” we invented solely to avoid the charge that it is illogical in the first place.

Overall, this book provides a helpful beginning to a discussion on the relationship between God and logic. It is a beginning, though, that leaves many questions unanswered—and some, in my opinion, wrongly answered. For those looking for a textbook about learning and using logic, I prefer the logic books already used by most logic teachers (e.g., Copi and Hurley).

Steven B. Cowan has contributed to several books and is associate professor of philosophy and religion at Louisiana College in Pineville, Louisiana.



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