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Trade Paperback
171 pages
Oct 2005
InterVarsity Press

Philosophy Made Slightly Less Difficult

by Garrett J. DeWeese & J.P. Moreland

Review  |   Author Bio  |  Read an Excerpt



Where Do I Start?

Ought not a Minister to have, first, a good understanding, a clear apprehension, a sound judgment, and a capacity of reasoning with some closeness?

We live in what may be the most anti-intellectual period in the history of Western civilization. . . . We must have passion—indeed hearts on fire for the things of God. But that passion must resist with intensity the anti-intellectual spirit of the world.

“I just don’t understand you. How can anyone with your education, who reads as much as you, believe the things you believe? How can you possibly believe in God, a kindly ‘grandfather-in-the-sky,’ when you see the suffering in the world caused by AIDS and tsunamis and famines and wars? You understand a lot about modern science—how can you deny evolution and believe there is anything more to the ‘real you’ than your body and your brain? You must know that miracles—violations of the laws of nature—are impossible. How can you believe that ‘spooky’ things like angels and demons are real? And your claims to know absolute truth—don’t get me started! Given everything we know about all the different religions and cultures in the world, how can you be so arrogant to believe that any one religion or morality is true and not merely a useful, culturally constructed fiction?”

Versions of these challenges to Christian faith are replayed repeatedly, day after day; doubtless, you have encountered them in some form. And if you have thought about the challenges much, you have thought philosophically. For the nature of the challenges is not really scientific or theological or anthropological, but philosophical.

Indeed your philosophical thinking probably started long ago. At some time you asked yourself whether or not something was real or what was real. You asked what or how you know something. And you asked what was the right thing to do in some situation or how you should live your life. These questions lie at the heart of philosophy.

So what is philosophy? Philosophy is thinking critically about questions that matter. Conceived this way, philosophy is something everyone does. Everyone has beliefs about what is real, what is valuable and how we come to know such things. For most people, such fundamental beliefs  re largely unexamined and perhaps even mutually inconsistent, but in forming such beliefs and acting on them, everyone is doing philosophy.

At a more developed level, “philosophy” refers to a body of knowledge, often the subject matter of college courses, which organizes and resents the thinking of major thinkers throughout the ages about such things as reality, values and knowledge.

At a still more refined level, “philosophy” is the specialized activity engaged in by certain “professional thinkers” who build on the thought of those who have gone before, utilizing certain tools and methods, with the goal of developing, presenting and defending carefully examined conclusions about reality, values and knowledge. Since philosophy is above all concerned with discerning the truth about these things, it is natural that philosophy has influenced every corner of life—both inside and outside academia—and that philosophical terms, tools, arguments and conclusions can be found in almost any book pulled from the library shelf.

Unfortunately the terms and tools are sometimes misused, and the arguments and conclusions often misrepresented. As with any discipline, the professional can quickly spot the errors, but to the untrained eye, all appears as it should.

We are deeply concerned about the impact of philosophy on theology. The medieval theologians believed that theology was the queen of the sciences (that is, of domains of knowledge) and philosophy was her handmaid. The development of theology in both the Eastern and the Western churches has been deeply affected by philosophy, and theology in turn has affected Western philosophy. But since the Enlightenment, roughly, the flow has been one-way, from philosophy to theology, and for the most part it has been corrosive to orthodox theology.

In our day, theology has largely been banished from the university (even many Christian colleges have reduced the required credits in Bible and theology), and philosophy has been largely ignored (liberal arts curricula in general have been weakened to make room for more “practical” courses). Couple this with a trendy anti-intellectualism in many evangelical churches, and the result is that most young women and men who desire to enter seminary or join the staff of a parachurch ministry are illprepared to understand and engage the philosophical aspects of biblical studies, in particular, and the culture in which they minister, in general. And most pastors have neither the time nor the background to keep up with trends in contemporary philosophy, even where it has a direct bearing on theology and ministry.1

Our goal in this “philosophical tool kit” is to redress this problem by providing you with a brief, nontechnical, practical guide to selected philosophical terms and concepts and to illustrate their importance and usefulness in teaching the Bible and doing theology in light of contemporary ssues.2 We are not aiming at making you a professional philosopher. But we do want you be able to recognize and understand the philosophy which you come across every day so that you can be more philosophically discriminating, whatever your particular path of service to our Lord.


We have often (too often!) heard someone say, “Why is logic so important in theology? You make it sound like logic is even over God!” We believe the question reflects a common misunderstanding of logic. If God did not exist, then logic would not exist (nor would anything else, for that matter). But if God does exist, then a whole lot of other things also exist, including the laws of logic.* For example, consider the law of identity: God is who he is, and not another God. Consider, too, the law of noncontradiction: God cannot be both good and notgood. These laws (and other things that exist timelessly) would not exist if God did not exist, so they depend for their existence on God. But they were not created by God in the sense that he could have made them otherwise. So to say that the laws of logic apply to God is not to make logic sovereign over God. It is simply to recognize that once something exists, then many other things also exist which cannot be any other way.

Another objection we hear often is this: “Well, there are many different logics. How can we tell which one is the right one? Isn’t that pretty arbitrary?” Again, we believe, this rests on a misunderstanding.

The short answer is yes, there are many different logics. But we should keep two points in mind. First, there are also many different algebras and many different geometries. (Mathematicians and logicians are quite creative!) Some of these different systems were devised for dealing with specific problems and do not claim universal validity (e.g., “fuzzy” logic, versions of multivalent logic and many systems of abstract algebra). Second, none of these systems could have been “built” apart from certain fundamental “laws of thought.” (If the law of noncontradiction did not hold universally, we could not even claim that there were different systems!)

A final objection goes this way: “Your logic is a relic of the maledominated West, and it ignores Eastern logic and feminist logic, for example.” Again, we believe this reflects a deep misunderstanding. With regards to “Eastern logic,” there really is no such thing. It is true that certain strands of Hinduism and Buddhism teach that contradiction lies at the heart of reality, that on the path to enlightenment one must learn to embrace contradiction. But as Mortimer Adler pointed out, as long as Hindus and Buddhists accept the results of modern science and technology, they are tacitly affirming the law of noncontradiction, which lies at the very foundation of science.3

As for “feminist logic,” this is almost certainly a matter of emphasis and values, not different logics. We may grant, for the sake of argument, that women are in general more relational and more emotionally connected, and men more objective and linear in their thought. But of course women can use objective logic when required, and men can learn to value relationships and emotional connections. Difference in emphasis is not difference in kind.

The laws of thought. Three logical laws are so fundamental that they are sometimes called laws of thought. We’ve already mentioned two of them, the law of identity and the law of noncontradiction. The third is the law of the excluded middle.

These laws are sometimes called axioms or fundamental principles. They cannot be proved, but their truth is inescapable, for as soon as you try to disprove any one of them, you find you must assume it. Suppose, for example, you were to try to disprove the law of identity. Then you assume you are trying to disprove the law of identity and not the law of gravity; the law of identity is what it is, and it is not the law of gravity. Or suppose you were trying to disprove the law of noncontradiction. That is, you’d be trying to prove that it was false that something could not be both true and false at the same time and in the same way. But that, of course, assumes the very law you’re trying to disprove. (There’s a famous story about the great Princeton logician Saul Kripke. In a meeting of faculty from other departments, several were trying to argue that the law of noncontradiction should be done away with, as it was a relic of male-dominated, Western, polarizing thinking. Kripke replied, “Good, let’s get rid of it. Then we can keep it too.”)

Do these laws have anything to do with theology? Most certainly! In Isaiah 45:5, for instance, God makes a strong claim: “I am the LORD, and there is no other; apart from me there is no God.” Now, according to the law of identity, it is Yahweh (the Lord) who speaks, and Yahweh is not Krishna or Brahmin or Baal. According to the law of noncontradiction, the Lord cannot be the only God and also just one of many gods. And according to the law of the excluded middle, either it is true that the Lord is the only God, or it is false; it cannot be the case that “the Lord is the only God” is true for Christians but false for Buddhists. (For more on the law of identity, see chapter two.)

Arguments. A philosophical argument is not a heated quarrel, nor is it a rhetorical contest. Philosophical arguments are not decided on the basis of majority vote or how someone feels about an argument. Arguments in philosophy consist in a set of premises which lead to a conclusion. There is a fundamental difference between deductive and inductive arguments. Below, we’ll examine inductive arguments, but here we’ll deal with deductive arguments specifically. In a deductive argument, the relation between the premises and the conclusion is a logical matter. The truth of the premises guarantees the truth of the conclusion; or, put differently, if the premises are true, the conclusion must be true. Still, not just any old set of premises together with a conclusion form a good argument. A successful argument— one which persuades someone of a true conclusion—must be valid, sound and cogent.

Validity. An argument is valid if its form is correct, that is, if the conclusion follows from the premises according to the laws of logic. An argument which does not have a correct form is invalid, even if the conclusion is true. Here’s an example of an invalid argument:

1. Some politicians are liars.

2. Jessica is a not a politician.

3. Therefore, Jessica is not a liar.

Even assuming that Jessica is not a politician, (3) doesn’t follow from (1) and (2). Here’s another example:

4. If Jupiter is the fifth planet from the sun, then it is the largest planet.

5. Jupiter is the largest planet.

6. Therefore, Jupiter is the fifth planet from the sun.

Even though each of the premises and the conclusion is true, this is an invalid argument because its form is incorrect. We say that the argument commits a formal fallacy. Shortly we’ll explain what is wrong with the form of these two arguments (if it isn’t apparent to you already). The point is that the validity of an argument depends on the form of the premises and the conclusion, not their truth.

Soundness. Why worry about validity? Simple. The conclusion of a valid argument is guaranteed to be true if the premises are true. An argument which has a valid form together with true premises is called sound. The conclusion of a sound argument is guaranteed to be true. So it is very important, in evaluating arguments, to insure the argument has the proper form (validity) and the premises are true (soundness). Of course, it is not always apparent whether or not a premise is true, and often it may be very difficult to tell. So philosophical arguments generally spend most of the time trying to show in some way that the premises are indeed true (or, at the very least, are more probable than their denials). And that leads to the issue of cogency.

Cogency. A cogent argument is one for which the validity and soundness are apparent to the reader, and so she accepts the conclusion of the argument. Unfortunately, this complicates things. No conclusion can be stronger than the strength of the weakest premise, and it frequently happens that we think we have stronger reasons to reject a conclusion than to accept at least one of the premises. In that case, even if we cannot demonstrate the falsity of a premise, and even if the argument is valid, it will not be cogent for us. It will not demand acceptance; it will not compel belief. Cogency, then, is person-relative. Many factors—psychological, personal, volitional, prejudicial or theological (think of original sin or the work of the Holy Spirit)—enter into the mix when a person evaluates an argument. Especially in the case where the premises are not clearly and undeniably true, a perfectly valid argument may lack cogency for someone. Some arguments are so complicated, the logic so sophisticated, that only specialists are able to grasp them. Such arguments may lack cogency even for the average philosopher. In part this explains why two people can look at the same argument and disagree completely about whether or not it is a good argument.†

There are a couple of reasons why this is important. First, you may be deeply convinced that a particular argument for, say, the existence of God is sound, but you find that someone—a very smart friend, perhaps—rejects it. That doesn’t automatically mean the argument is a bad argument and you should give it up. Rather, there may be other factors at work in your friend’s life that make it more plausible to him to deny the conclusion that God exists than to accept the validity of the argument or the truth of the premises, even if he can’t say just where the argument went wrong.

Second, you may encounter an argument in your study which leads to a conclusion that you find dead wrong. It just isn’t cogent for you. If you have stronger reasons to reject the conclusion of the argument than you do to accept its soundness, you are within your intellectual rights not to accept the conclusion. But—and this should go without saying—the fact that we don’t like a particular conclusion is not in itself a sufficient reason to reject it. We must be honest with the argument and with ourselves, and sometimes that means doing some hard thinking and research to discover just where the argument went wrong. Or we may discover that we were wrong and accept the conclusion after all.

One final matter before moving on has to do with the notion of certainty. Sometimes authors use the term certain to refer to a proposition that is infallible (such as the proposition that “Anything that is red is colored”). But more often, and in the general population, certainty is a psychological predicate, indicating that someone believes a proposition and entertains no doubt about it. We have all been certain about some false propositions (and in all likelihood we are right now as well). “Certain” often serves a rhetorical purpose in an argument, and just because an author labels a premise as certain does not mean it is beyond question. In short certainty belongs to persons, truth to propositions.

Valid forms of deductive arguments (and associated fallacies). We begin this section with a caveat: this is not nearly a complete survey of valid argument forms.4 Nevertheless, there are a few which merit attention. In what follows the letters p, q and r represent propositions (for now, think of a proposition as a declarative sentence). Several of the forms use an if, then form: If p, then q. This is called a conditional statement; p is called the antecedent, and q is called the consequent. In addition, we’ll use the standard symbol ~ (the tilde) to stand for not. For each form below we’ll use both symbolic notation and provide an example. For the sake of illustration we’ve used simple examples, but most arguments you encounter will not be so simple. See if you can think of other more complicated sentences to substitute for p, q and r and reflect carefully about the resulting argument.

Modus ponens:

If p, then q If Mary has a sister, then Mary is a sibling.

p Mary has a sister.

Therefore q Therefore Mary is a sibling.

Modus ponens is perhaps the most intuitively obvious inference pattern; anyone who thinks about it will see that it is clearly valid.

The associated fallacy is that of affirming the consequent. One states a conditional, claims that the consequent is true and concludes that the antecedent must be true. But this is clearly invalid:

If p, then q If Mary has a sister, then Mary is a sibling.

q Mary is a sibling.

Therefore p Therefore Mary has a sister.

(Of course, Mary could be a sibling who has only brothers.)

Modus tollens:

If p, then q If Mary has a sister, then Mary is a sibling.

~q Mary is not a sibling.

Therefore ~p Therefore Mary does not have a sister.

The associated fallacy here is denying the antecedent. Again, the fallacy should be clear:

If p, then q If Mary has a sister, then Mary is a sibling.

~p Mary does not have a sister.

Therefore ~q Therefore Mary is not a sibling.

Hypothetical syllogism:

If p, then q If it’s snowing, then it’s below 32°.

If q, then r If it’s below 32°, then it’s cold.

Therefore if p, then r Therefore if it’s snowing, then it’s cold.

Disjunctive syllogism:

p or q Either Bill is in his apartment or he is out.

~p Bill is not in his apartment.

Therefore q Therefore Bill is out.

Here the or statement (called a disjunction) is assumed to be true. So if one of the terms (“disjuncts”) is false, the other must be true. There’s an associated fallacy here also, but it is not a formal fallacy—that is, it is not a matter of an incorrect form. It’s the informal fallacy of false dilemma:

p or q Either Bill is in his apartment or he is in the library.

~p Bill is not in the library.

Therefore q Therefore Bill is in his apartment.

Remember that the truth of the conclusion depends on the truth of the premises. A disjunctive syllogism relies on an exclusive sense of or such that the two alternatives are the only ones possible. The disjunction “p or q” is true if and only if p is true, or q is true, or both are true. If, in our example, it is possible that Bill is en route, then the conclusion will not follow. In such a case, where the disjunction “p or q” does not express mutually exclusive possibilities, the premise presents a false dilemma.

We have pointed out only four of nine rules of inference which determine valid deductive argument forms, but these are perhaps the four most common. (As an exercise, see how many you can identify in the editorial section of Sunday’s newspaper.) We’ve also noted two associated formal fallacies and one informal fallacy. As might be expected, it turns out that there are many ways an argument can go wrong even if it is in the correct form. These ways are called informal fallacies. There is no complete list of informal fallacies, perhaps because there is no end to the creativity of illogical people! But the following survey should be helpful in recognizing common informal fallacies (in addition to false dilemma, discussed above).