One of the most common mistakes I see in logic instruction in many schools is to begin teaching it by having students study informal fallacies. It’s not that it does them any damage; it just doesn’t do them as much good as many educators seem to think.
The Two Kinds of Logic
There are two kinds of fallacies which correspond with the two kinds of logic, formal and informal (or “material”).
Formal logic studies the hard-and-fast rules having to do with how to argue. It doesn’t address anything specific about what you are arguing about—it merely shows you how, given any set of premises, true or false, you can reason well. Of course, if you have bad premises, even valid reasoning won’t get you far, but it is important to be able to isolate the formal (or mechanical) aspect of reasoning so that you can study it by itself in order to understand it better and perhaps fix it.
Informal (or material) logic has to do, not with the mechanism or procedure of logic, but with the material or content aspects of words, statements, and arguments. Formal logic also deals with these things, but only with that aspect of them that directly affects how a formal argument works. Informal logic deals with the different kinds of arguments and statements, and the diverse meanings of words, the different ways you can say something about something else, and the types of arguments according to their use.
In informal logic, unlike formal, it does matter what you are arguing about and how much you are trying to prove.
When we go to cook a meal, we may use a recipe, which not only has the ingredients we are to use, but the instructions on how to put it together. The procedure for putting the ingredients together is like the formal aspect of logic, and the ingredients themselves are like the material or informal aspect of it. Both affect the outcome of the recipe (or argument), but in different ways.
Let’s say I argue:
All men are mortal
Socrates is a man
Therefore, Socrates is mortal
Whether the last statement logically follows from the first two (regardless of whether either of the first two are true), is a question of formal logic. What is referred to by “men,” “mortal,” and “Socrates” is a question of informal logic.
The Two Kinds of Fallacies
A failure to reason rightly involves formal fallacies. These are just the violations of the formal or mechanical rules of argument. The Fallacy of Undistributed Middle just means that the two things connected together in the conclusion were not properly connected in the premises; the Fallacy of Illicit Process just means that you said more in your conclusion than was justified by your premises; and so on.
But informal fallacies are different. They do not violate formal rules, but informal ones—the ones that have to do with the kind of words you use and the kind of statements in your argument—things extrinsic to the structure of the argument. Rather than logical rules, they violate linguistic, or psychological, or epistemological, or statistical rules.
These would include fallacies like that of composition (that what is true of the parts must be true of the whole) and ad hominem arguments (those that confuse a point with a person, that a person is bad rather than that a person is wrong, etc.).
Should Fallacies Be Taught First?
Why do so many logic instructors want to begin their study of logic with informal fallacies?
The most common reason teachers give for teaching fallacies first is that informal fallacies are fun to study. In our entertainment-oriented culture, this can seem like a sufficient reason for doing something. Assuming it is true that fallacies are fun, the level of immediate gratification a student gains should never be considered a sufficient reason for an educational pursuit. It would be a fallacy to say that what is fun is necessarily a good use of education time.
We can put this in the form of a logical dilemma: Either a fallacy is easy to understand, in which case it is fun but there is not much educational benefit to identifying examples of it, or it is difficult to understand, in which case students with no prior training in logic will find it difficult, and hence not fun. So teaching fallacies first either doesn’t bring much benefit or isn’t much fun.
In most classrooms, instructors will describe a particular fallacy and then let their students loose on the world to collect a few more, like bugs for an insect display. Although this exercise does develop the ability to identify examples of bad reasoning, it does this only in the sense that they recognize its obvious outward features. This is all fine, but it doesn’t give any direct help to a student in understanding what good reasoning is—nor can students even gain a very good understanding of why they are fallacies in the first place.
Informal fallacies are both easier and more difficult than formal fallacies. While an understanding of formal fallacies requires an understanding of formal logic that is difficult to attain, once one knows the rules, it is easy to spot a deviation from them. Informal fallacies, on the other hand, can be identified easily, but because they involve more intricate and subtle linguistic and psychological problems, an understanding of why they are fallacies at all remains a mystery to the average middle school student (the age level at which they are often taught).
Nor does an ability to merely identify informal fallacies help in real-life argumentation. Just charging your opponent with committing a “Red Herring” doesn’t really impress an audience. In most cases, they will have no idea what you are talking about. Real-life argumentation requires a deeper and more important understanding of why such reasoning is bad, so that, in a debate, the student is able not just to name his opponent’s mistake in reasoning, but to draw an analogy to the reasoning his opponent has used so the audience can see how inadequate it is. This requires a mastery of the analytic skills necessary to do this, which is not available by merely studying informal fallacies.
Formal logic is ideal for students—not only because it trains them in the analytic skills needed for understanding other aspects of logic (like informal fallacies), but because, by its nature, it is organized and systematic. One need merely master certain very straightforward processes that ease students, in a straightforward and systematic way, into abstract thought.
When I am asked by parents and teachers what they need to do as a preparation for formal logic, I do not recommend informal fallacies. Rather, I tell them that their students need to study math and Latin, which together offer the best preparation for the analytic thought required in formal logic.