Basic Logic for Apologetics

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“Christianity is just not logical!”

A friend of mine who serves in Spain began to encounter this objection when he tried to talk about faith in Jesus Christ. He wrote to me and asked how he could respond. To commit your life to something that is illogical is a serious charge. If Christianity is truly illogical it calls into question how we can expect modern people to believe it. Even more, it raises the question of how we can believe it ourselves. Is the gospel truly against logic?

The answer lies in the nature of logic itself. Logic is one of the powerful tools of apologetics. Logic has the power to expose contradictions in both our thought and the belief systems of unbelievers. Christians are often viewed as illogical and irrational by unbelievers who put great emphasis on rationality, logic, and scientific precision. While it is true that Christians can be illogical and irrational, the Christian faith is neither of these things. The Christian faith is the only belief system that truly reflects the nature of the world and truth as it is. All other belief systems are denials or distortions of the truth.

One of the most powerful ways to defend the Christian faith is to identify and refute logical fallacies in the objections raised against the Christian faith. This requires, first of all, that our own reasoning is marked by true and sound thought. In this chapter we will learn the basics of logical thinking and how logic can help us see through the false beliefs of unbelievers we meet.

The Basics of Logic

Logic is the art and science of reasoning well. More formally, it is “the study of the methods by which the conclusion is proved beyond all doubt.”[1]In other words, logic is what distinguishes between what is not true, what may be true, and what is necessarily true, given the facts. Logic helps us avoid contradiction and irrationality. It also keeps us from allowing incidental or unimportant factors from interfering with our quest for the truth. For example, whether I like something or not, if it is true, I should believe it. Whether I like the person who is telling me a fact, if the fact logically follows from the evidence, I should believe it.

The Elements of Logical Argumentation

To ensure that our thinking is logical, we must understand the basics of logical argumentation. First, the most basic building block of logical thinking is a sentence. A sentence is a complete grammatical thought. Sentences can be short, such as, “Run!” or “Will you?” As long as a subject and verb are present in the proper relationship, you have a sentence.

proposition or statement, on the other hand, is a sentence that affirms or denies something, and can be true or false. “God exists” and “The universe is not eternal” are both propositions that can be used as part of an argument. A syllogismis a kind of logical argument in which one or more propositions are combined to result in a conclusion, or inference. When propositions are used in a syllogism, they are called premises.

An argument consists of at least one syllogism, and often several syllogisms strung together. An argument “is what results when someone advances a claim or series of claims as evidence for the truth of another claim.”[2]What we seek to present in apologetics are arguments that persuade unbelievers toward the truth.

So, to summarize, an argument is a claim for truth and consists of one or more syllogisms, in which the conclusion necessarily arises from the premises.

For example, here is an example of a famous syllogism:

Premise 1: All men are mortal.

Premise 2: Socrates is a man.

Conclusion: Socrates is mortal.

This syllogism consists of two premises that necessarily result in the conclusion (inference). In a syllogism, the truth of the premises is assumed to already be established. If it is true that all men are mortal, and that Socrates is a man, then it necessarily follows that Socrates is mortal.

Even though such words are not used in the example above, sometimes connecting words are used to show more clearly the necessary nature of the conclusion. For example, the conclusion could read, “Therefore, Socrates is mortal,” or “Because all men are mortal, and Socrates is a man, consequently, Socrates is mortal.” Connecting words such as “thus,” “because,” and “therefore” don’t always show up in formal syllogisms like the one above, but we do tend to use them when we speak.

In normal conversations people don’t speak in syllogisms.  They don’t say, “Premise 1: Ice cream costs $4.00. Premise 2: I have $4.00. Conclusion: I have enough money for ice cream.” Rather, we tend to think informally and arrive at such conclusions without working through the logic explicitly in our heads.

In the next post we will look at the value of logic for apologetics.

[1]Gordon Clark, Logic(Trinity, 1988), 1.

[2]Stephen Carey, The Uses and Abuses of Argument: Critical Thinking and Fallacious Reasoning(Mayfield, 2000), 3.

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