Logic Primer 1: What Is Logic?

Logic studies the methods that we use to analyze information and draw valid conclusions. As Norman Geisler and Ronald Brooks put it, “Logic really means putting your thoughts in order.”1 They offer their formal definition: “Logic is the study of right reason or valid inferences and the attending fallacies, formal and informal.”2 Their simplified definition: “Logic is a way to think so that we can come to correct conclusions by understanding implications and the mistakes people often make in thinking.”3

According to Irving M. Copi and Carl Cohen in their Introduction to Logic, “Logic is the study of the methods and principles used to distinguish correct reasoning from incorrect reasoning.”4 Christian philosopher Gordon Clark puts it succinctly: “logic is the science of necessary inference.”5

We can see from these definitions that logic consists of ordering our thoughts so that we can reason correctly. Geisler and Brooks would add: “The next best thing besides godliness for a Christian is logic”6

The study of logic incorporates a number of elements. At the most basic level, logic examines propositions, arguments, premises, and conclusions. The focus is the use of right thinking to come to correct conclusions. Logic incorporates the study of proper thinking as well as mistakes in thinking (fallacies). Through processes of deduction and induction, inferences are made with the aim of coming to correct conclusions.

In addition, logic also deals with our use of language. The logical thinker is very concerned about precision and clarity in communication. He is concerned with the proper structure of arguments and the correct flow of thought. The student of logic seeks to be careful, methodical, and systematic.

Logic is built upon four undeniable laws:
1. The law of non-contradiction (A is not non-A)
2. The law of identity (A is A)
3. The law of excluded middle (either A or non-A)
4. The law of rational inference

These undeniable laws are foundational to all reason and thinking. One cannot object to the laws of logic without using them in his objection. Where did they foundational laws come from? Geisler and Brooks offer a Christian perspective: “From the standpoint of reality, we understand that God is the basis of all logic. As the ultimate reality, all truth is ultimately found in him.”7

In the next section, we will deal with the building blocks of logic. Terms will be defined and the basic foundation will be laid for further study.

Here are some resources that will get you started:
Audio resources:
- Princeton Review's LSAT Logic in Every Day Life podcast
- Reasons to Believe's Straight Thinking Podcast
- Greg Bahnsen's Critical Thinking course (logic) - uses Copi's textbook. Good only if you are using the book, but audio quality is poor.)
Helpful books:
- Copi and Cohen's Introduction to Logic - recommended for the serious student.
- Being Logical by D.Q. McInerny - recommended as the first read.
- Come Let Us Reason by Norman Geisler & Ronald Brooks
Some Web Links:
- Wikipedia on Logic
- Ken Samples article: Keep your thinking on track.
- Take a logic test here.

Tomorrow we look at the Building Blocks of Logic.

1 Norman Geisler & Ronald Brooks, Come Let Us Reason: An Introduction to Logical Thinking (Grand Rapids, MI: Baker Books, 1990), p. 11.
2 Ibid., p. 12.
3 Ibid.,p. 13.
4 Irving M. Copi & Carl Cohen, Introduction to Logic, 11th Edition (Upper Saddle River, NJ: Pearson Education, 2002), p. 3.
5 Gordon Clark, Logic (Jefferson, MD: The Trinity Foundation, 1985), p. 1.
6 Geisler & Brooks, p. 7.
7 Ibid., p. 17.