In her essay “The Lost Tools of Learning,” Dorothy Sayers has identified for many classical Christian schools of our day an outline for a modern education following the medieval Trivium: Grammar, Logic, and Rhetoric. I am interested in what she says about Logic and the Dialectic Stage, and plan to occasionally post some thoughts about these and related topics. I will start my posts with a comment she makes that I have found helpful in my own teaching of Logic.

In describing a student of the medieval Trivium, Sayers writes, “Secondly, he learned how to use language; how to define his terms and make accurate statements; how to construct an argument and how to detect fallacies in argument.” This short statement gives us what I have come to believe are the four primary lessons to be learned in a Logic class, and in the proper order.

First, the logic student learns about terms, which are the building blocks of statements. They learn what a term is, how terms differ from words, the methods and rules of defining terms, and how to use the tools that relate terms to one another, such as genus and species charts.

Second, the logic student learns about statements. They learn what a statement is, how to identify the different types of statements, how to relate statements to one another, and how to determine the truth of a given statement.

Third, the student learns “how to construct an argument.” Logical arguments are built out of statements, which are connected as premises to make conclusions. Students learn how to distinguish between valid and invalid arguments, what validity means, and why it differs from truth. Once they are able to identify valid arguments given to them, they learn how to construct valid arguments of their own.

Fourth, the logic student learns “how to detect fallacies in argument.” A fallacy is an invalid form of argument. They learn to identify not only the formal fallacies discovered by the rules of validity, but also informal fallacies such as ad hominem and post hoc.

Thus, Sayers has given us the outline of a complete introductory logic curriculum. I would only add that we should not limit our learning of the above to categorical logic, but include the tools of propositional (or symbolic) logic as well. Students should be given the powerful tools of relating symbolic propositions, determining the validity of propositional arguments, and learning how to construct propositional proofs.

In our doctrine class we discuss classical arguments for and against the existence of God. One such argument is the Problem of Evil and goes something like this: “If God exists, then he is both perfectly good and infinitely powerful. If he is perfectly good, then he is willing to prevent evil. If he is infinitely powerful, then he is able to prevent evil. But if evil exists, then God is neither unwilling or unable to prevent it. Evil does exist. Therefore God does not exist.” We use a shorter truth table to show that this argument is indeed valid (or perhaps we write a proof for it). The students who have taken logic know that if an argument is valid, but the conclusion is false (as this obviously is), then at least one of the premises must be false. This leads to a fruitful discussion about which premise is false, and why. Is God infinitely powerful but not able to prevent evil because he cannot interfere with the free will of men? This is the choice of many modern evangelicals. Does God’s perfect goodness require that He is always willing to prevent evil? Reformed scholars would say no, and give counterexamples such as the crucifixion.