For twenty centuries, Christian thinkers have emphasized the importance of logic. They have recognized logic as one element of God’s very essence. John 1:1, “In the beginning was the Word, and the Word was with God, and the Word was God,” points to that truth. The Greek word there translated “Word,” Logos, has a range of meanings that include logic, account, reason, and argument. (In fact, in John’s day, it rarely denoted a single word.) John 1:1, then, reveals that God is logical—not that He is bound by laws external to Himself, but that those rules are of His very essence.

In generations long past, education in Western Civilization usually began with the trivium(grammar, logic, and rhetoric), then proceeded to the quadrivium (arithmetic, geometry, music, and astronomy), followed by various other subjects (history, philosophy, theology, etc.). The trivium provided students with the basic skills they needed to learn the quadrivium, and the quadrivium in turn provided the tools needed to learn other subjects. The role of logic was to equip students to reason properly from premises to conclusion—and to detect when others were, or weren’t, doing so.

Very few elementary and high schools, at least since the mid-twentieth century, even offer logic, let alone include it in required curriculum, and almost no colleges require it for any major other than philosophy.

The sad result is a steep decline in people’s ability to reason properly and detect unreason. Yet the need to understand logic is universal because the odds that we’ll argue fallaciously and thus deceive or be deceived if we don’t are high. How high?

Well, take one type of argument, categorical syllogisms, for example. These are arguments in forms like “All men are mortal. Socrates is a man. Therefore Socrates is mortal,” or “No fish are mammals. Some vertebrates are mammals. Therefore some vertebrates are not fish.” The terms “men,” “mortal,” and “Socrates” can be incorporated into 256 different types of syllogisms—and of those, 232 (over 90%) are invalid—meaning that their conclusions don’t follow logically from their premises. If you don’t know the rules of the syllogism, the odds are good that whatever argument you construct will be invalid. (Okay, maybe this is just for nerds, but in case you’d like to see a complete chart of the 232 invalid and 24 valid forms, click here!)

An enormous amount of discussion and argument about environmental stewardship, especially about such highly controversial and emotionally charged topics as climate change and climate and energy policy, especially in the political sphere, consists largely and sometimes wholly of logical fallacies. Though we’re not infallible, we at the Cornwall Alliance try to keep our reasoning valid (that is, not fallacious), and we’d like to recommend some tools the study of which will help you do likewise.

So, we’ve posted a 4-page “Summary of Major Concepts, Principles and Functions of Logic” that you can use as a checklist and memory aid as you study logic. It includes such things as:

• The three laws of thought
• The rules of definition
• The rules and fallacies of categorical syllogisms
• The rules of immediate deduction
• The rules of the 5 (and there are only 5) possible (and 2 impossible) relationships between categorical propositions that use the same terms
• The “Square of Opposition” illustrating those 5 relationships
• The rules and fallacies of hypothetical arguments (i.e., of the form “If what Smith just drank is a deadly poison, he will die within 24 hours. Smith lives another 24 years. Therefore what Smith drank wasn’t a deadly poison.”)
• The rules and fallacies of 5 other common forms of argument
• A long list and explanation of some of the most common informal fallacies:
  1.  Fallacies of Relevance (21 types!)
  2. Fallacies of Ambiguity (10 types)
  3.   Reductionist Fallacies (5 types)
  4. Procedural Fallacies (7 types)
  5. Metaphysical Fallacies (6 types)
  6. Others (5 types)

And here are three book recommendations:

• Norman L. Geisler and Ronald Brooks, Come, Let Us Reason: An Introduction to Logical Thinking, a clear, concise introduction with exercises and answer key that anyone can use for self-study
• Peter Kreeft, Socratic Logic: A Logic Text Using Socratic Method, Platonic Questions, and Aristotelian Principles, a work that focuses on informal fallacies
• H.W.B. Joseph, An Introduction to Logic, 2d ed., an in-depth and advanced work mastery of which should be the goal of anyone who wants to be really proficient in logic, also available free in PDF

So join the club of those committed to logical thinking! If we all do that, our discussions will be both more enlightening and more peaceful.