Come, Let Us Reason: An Introduction to Logical Thinking

This is an adequate introduction to logic. It explicates the subject well and is therefore a very useful teaching tool. The content and examples are clearly intended to appeal to a conservative Christian audiences. Now, to address some online ‘nitpicking’ about the text: The reviewer Daniel J. Paszak “Diogenes” has correctly pointed out that, despite one of the examples in the text, the rules of standard logic dictates that when the conclusion of an argument is a tautology, that argument is considered valid by default. While this seems counter intuitive (since it is natural to assume validity has to do strictly with how premises “force” a conclusion), it is nonetheless true. Anyone can google this fact. To understand why this is true, one can simply refer to a truth table, and note that the expression “P implies Q” is true whenever Q is true; therefore, if Q is a tautology, the statement is always true no matter the premise. Similarly, if P = A and B, then the sentence translates into a syllogism: Premise 1: A Premise 2: B Conclusion: Q Given the rules of implication dictated by the truth table, this syllogism would be valid whenever Q is a tautology. If the definition of validity is “given the rules of inference, the conclusion is true whenever the premises are true”, then this fact holds perfectly. One reviewer has incorrectly depicted this tiresome nitpicking as “spiritual warfare” and incorrectly suggests that the reviewer mentioned above confuses validity for truth. The reviewer Daniel J Paszak “Diogenes” was also correct in pointing out that (at least an earlier edition of) the book had, presumably, a misprint whereby the statement -q or -p is equivalent to -(p or q). Clearly, it is not. However, the reviewer was not suggesting that the book was “claiming” this to be true, as if the author is unaware of De Morgan’s Law. It was clearly a misprint - but perhaps a significant one.

This book is not meant for casual reading (you have to think to understand this one), but it can help enlighten the casual reader (who does not want to study) if he/she skims through the first 90 pages (which require some study of terms and differences)and then coasts through the rest. Geisler and Brooks are Christian thinkers who understand thinking and logic, and they present the major components of logical thinking in a Christian context.   The authors explain syllogisms and differentiate between a valid conclusion and an invalid conclusion. They also distinguish validity from actual truth (valid conclusions are not always actually true in reality; they are merely logically based on the premises presented).  That's the stuff addressed in the first 90 pages.   But the best part (and most enjoyable for me)began with chapter 6, "Informal Fallacies."  This section was lighter reading. Since this is an election year, it would be a study in itself to compare political commentaries and supposed answers to questions with the logic presented in this volume!    Since the authors are serious students of Scripture and Geisler is a celebrated Theologian, most of their examples come from familiar Bible texts or theological issues. Although I have stronger convictions about Sovereign Grace than do the authors, I really found their examples useful in the realm of hermenutics (Bible interpretation). They are solid defenders of an inerrant Bible and ethical interpretation.   If you want to brush up your thinking skills, this might be a good place to start. "Fit Bodies, Fat Minds" by Os Guiness persuades us that the use of the mind has been neglected in evangelical communities, and Geisler and Brooks have written a work to help properly activate those little grey cells. Not really an easy read, and not for everyone, but a meaningful mind stretcher.

The reviewer Daniel J. Paszak "Diogenes" criticizes this book because it claims that a tautology is invalid. If the reviewer, however, bothered to read p. 23, he'd see that "there is a difference between truth and validity." A conclusion may be true (such as a tautology, for instance), but if it does not follow from its premises, then the argument is still invalid. This is a standard logical system. See the definition of "valid" in Copi and Cohen, Introduction to Logic. Also, this book does not claim that "-p or -q" is "-(p or q)." Look again. The authors are not unaware of De Morgan's theorem. Furthermore, it exasperates me when reviewers like Truth seeker "a reader from NY" say that they are surprised to see that this is a book that assumes/promotes Christianity. Or when other reviewers like John L. Davis say that the use of biblical references is distracting. Duh! Look at the back cover and see what the book is about and who the author is! This is one of those "logic texts intended explicitly for Christians." Geisler is "one of evangelicalism's most prolific writers." This is a book written by two Christians for a Christian audience. And do you know where the title "Come Let Us Reason" comes from? (Hint: the Bible.) So don't gripe that this book assumes a Christian worldview. Now, for Christians: Anti-intellectualism is one of Satan's strategies that have made the church ineffective. Geisler's book combined with a good textbook on biblical hermeneutics will enable the Christian to recognize and combat deception and fallacies, and appropriate God's truth. By reading this book, you'll know what a "straw man fallacy" is. Accusing Geisler with something he didn't say is an example. Geisler in the book mentions paradox, but does he ignore it (See the the fallacious review by J. Kowalski "mumon")? Geisler only says that what is not paradoxical in theology should not be considered so. [The trinity is a mystery but NOT a paradox or a contradiction because it does NOT say 1 is equal to 3. God is 1 in an aspect (essence) and 3 in another aspect (person). Anybody who says Christians believe a contradiction is again guilty of straw man attack.] The reviewer also insinuates that Geisler holds that all truth is derivable from logic. However, Geisler is an evangelical and holds to truths revealed in the Scripture, not just truths derived from reason. You'll be able to recognize what a "faulty dilemma" (also called "false dichotomy") is. Saying that being human and God at the same time is contradictory is an example. And what is "dicto simpliciter"? It's the fallacy that applies a general rule to circumstances not included in the rule. The general rule that "Cretans are always liar" does not apply to Epimenides, so Paul is able to quote him and assert that "This testimony is true" (Titus 1:13). You'll also learn from this book what an "argumentum ab annis" is. It's the fallacy that says because a concept is oudated, it must be false. (Sounds familiar?)

The main strength of this book is its thorough catalog of informal fallacies, accompanied by a glossary for easy reference. Although overtly Christian in tone, it is suitable for anyone interested in informal logic.

The church is permeated with people propagating pious notions of anti-intellictualism. While the intellect is not the be-all-end-all of the Christian life it is one of the most often neglected aspects of santification. The mind in scripture is the only thing that we renew. God supernaturally gives us a new heart, but gives us the enormous and exciting responsibilty for the renewing of the mind. Logic is one major aspect of this renewal. While emotions are central those emotions must not be irrational. Geisler and Brooks provide the framework by which we can decern the fallacies of foolish thinking and grasp the essential role of Logic in the life of the Christian. This book along with J.P. Moreland fine work "Loving God with All Your Mind" will serve as an antidote for our neglect of the mind.

I recommend this not-boaring-at-all book to anyone who takes thinking seriously and wants a concise look into logic. This book is a must for those who have never studied logic, as it teaches how to identify correct and incorrect thinking. This book reads like a text book, as it gives you exercises to complete in order that you apply what you learn. Geisler looks at logic with Theology (his primary discipline) to clarify the rules of logic, which I don't think is a deterrent (to the unbiased), in that it does not detract from the study of logic itself, but rather gives us examples to sink our teeth into. There's plenty of incorrect thinking in our society, & this book helps one to see through the bad arguments proposed.