by Dr. Jason Lisle
Also available in Español

Logic is a very valuable tool, particularly for the Christian who wants to defend his or her faith better.

Whenever I hear people debating some issue (abortion, gun control, origins, religion, politics, etc.), I often spot a number of mistakes in their arguments. Mistakes in reasoning are called “logical fallacies,” and they abound in origins debates. I have often thought it would be fun to carry a little buzzer that I could push when someone makes a fundamental mistake in reasoning. Of course, that would be impolite. However, we should all become familiar with logical fallacies so that our mental buzzer goes off whenever we hear a mistake in reasoning.

Logic (the study of correct and incorrect reasoning) has become a lost skill in our culture. And that is a shame. It is a very valuable tool, particularly for the Christian who wants to defend his or her faith better. Evolutionists often commit logical fallacies, and it is important that creationists learn to identify and refute such faulty reasoning. Sadly, I often see creationists committing logical fallacies as well. There is hardly anything more embarrassing than someone who advocates your position, but does so using bad reasoning!

Logic involves the use of arguments. When some people think of “arguments,” they think of an emotionally heated exchange—a “yelling match.” But that is not what is meant here. An argument is a chain of statements (called “propositions”) in which the truth of one is asserted on the basis of the other(s). Biblically, we are supposed to argue in this way; we are to provide a reasoned defense (an argument) for the Christian faith (1 Peter 3:15) with gentleness and respect. An argument takes certain information as accepted (this is called a “premise”), and then proceeds to demonstrate that another claim must also be true (called the “conclusion”). Here is an example:

“Dr. Lisle is not in the office today. So, he is probably working at home.”

In this argument, the first sentence is the premise: “Dr. Lisle is not in the office today.” The arguer has assumed that we all agree to this premise and then draws the conclusion that “he is probably working at home.” This is a reasonable argument; the conclusion does seem likely given the premise. So, this is called a “cogent” argument. This type of argument is classified as an inductive argument because the conclusion is likely, but not proved, from the premise. (After all, Dr. Lisle could be on vacation.) If the conclusion were not very likely given the premise, then the argument would be considered “weak” rather than “cogent.”

The other type of argument is called a deductive argument. With this type of argument, it is asserted that the conclusion definitely follows from the premises (not just probably). For example:

“All dogs are mammals. And all mammals have hair. Therefore, all dogs have hair.”

The conclusion of this argument definitely follows from the premises. That is, if the premises are true, then the conclusion has to be true as well. So, this is a valid argument. If the conclusion did not follow for a deductive argument, then the argument would be invalid.

Over the next several weeks, we will explore the most common logical fallacies. It is very helpful to know these fallacies so that we can spot them when evolutionists commit them—and so that we do not commit them as well. In the Christian worldview, to be logical is to think in a way that is consistent with God’s thinking. God is logical.

As Christians, we have a moral obligation to think and act rationally—to line up our thinking with God’s truth (Ephesians 5:1; Isaiah 55:7–8). We pray that this logical fallacy series will be God-honoring, and will tremendously improve your defense of the faith.


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