We don't have to be on the high school or college debate squad to be logically consistent and valid in our argument. Most of the time, we use good logic and demand good logic from others. Sometimes, though, we get lazy and see that it is easier to play on someone's emotions than it is to debate on the trickier fields of intellectual play. We have to be as logically consistent and fair as we demand others to be. We can't try to get away with something in an academic paper that we would abhor in a political debate (or worse yet, in a political advertisement). In our writing, we must learn to look out for the rotten apples known as fallacies, bits of rhetorical fakery that just about every writer succumbs to from time to time. If our readers catch us in a fallacious statement or conclusion, our entire argument becomes flushable. Here are several of the most common fallacies. Most of them have fancy names — some even in Latin — which we ought to become familiar with.

Non Sequitur ("It does not follow")
Post Hoc Ergo Propter Hoc ("After this, therefore because of this")

These two fallacies are close cousins. We cannot assume that because something precedes a later development, the first event causes the later event. Causes not immediately evident to us and intervening causes between the first cause and final result may exist. Review the Cause and Effect Essay section for additional help.

"John and Mary became vegetarians last fall and they've been sick all winter. The absence of meat in their diets must have weakened their immune systems."

A lot of other things could have made John and Mary sick this winter. Maybe they've been around a bunch of sickly kids or they started working in a hospital and their immune systems aren't used to all those germs. Maybe their immune system is fine; they're just temporarily overloaded or tired. The non sequitur fallacy means that you've made a conclusion that is not justified on the grounds given. The post hoc ergo propter hoc fallacy means that you have concluded that because something happened earlier, it must be the cause of a later event. These two fallacies are similar to yet another fallacy known as Jumping to Conclusions or Hasty Generalization which means that the evidence provided is not yet substantial enough to warrant the conclusion we've arrived at.

Stereotypical Thinking

To indulge in stereotypical thinking means that your brain has slipped into idle; you're accepting as truth a tiresome, commonplace (if not downright idiotic) assumption about people. "Women make lousy drivers. Asians are naturally good at mathematics. Scottish people are tight with money. White men can't jump." The next time you meet a tall African American youth, ask him or her if he or she plays basketball. You'll deserve the icy stare you get in return. (Or ask Dwight Stones or Patrick Sjoberg why white men can't jump.)

"Vegetarians are weaklings. They don't have good muscle strength because they don't eat meat."

Guilt by Association

If something gets categorized with something else that is "guilty" of something awful, there is a tendency for everything to be tainted by the guilty party. Remember how unfair it seemed when Mother accused you of stealing Mrs. Young's necklace just because you hung out with Jerry Biggsloff, who she knew was up to no good?

"I read somewhere that most cults are made up of vegetarians. We know that cults are filled with kooks and weirdos. John and Mary are vegetarians so they must be weirdos."

Argument Ad Hominem ("To the man")

"To the Man" — sorry, but Latin is even more sexist than English — means that the writer attacks the character of his or her opponent rather than the opponent's ideas or argument. This is what politicians are good at, and radio talk-show hosts are even worse. As an exercise, count the ad hominem attacks used by Rush Limbaugh on a good afternoon as he piles up references to "feminazis" and "environmentalist whackos." A good hair-pulling, eye-gouging scrap on Saturday morning cartoons is fine, but it has no place in academic discourse. Stick to the issues.

"State Secretary of Health Saunders recommends vegetarianism. But Saunders is the same guy who hands out condoms at high school assemblies and he has been arrested on drunk driving charges. I think it's pretty obvious we shouldn't listen to Joe Saunders's advice on diet."

Circular Reasoning

Circular Reasoning is similar to a definition that restates the subject in its predicate: a computer virus is a virus that infects a computer.

"Vegetarianism is not healthy because it is not healthy to cut meat out of your diet."

Petitio Principii ("Begging the Question")

This fallacy has an enduring hold on our thinking strategies because it is so easy to fall into this habit. It is similar to the child-parent argument we've all heard before:

"Why because?"
"Because because!"
"Why because because?"
"Because I said so!"

An argument cannot be built on a premise that simply claims to be true but whose truth is not established.

"People who adopt vegetarianism as a lifestyle are asking for health problems. Therefore, the Office of Student Services should set up a nutrition program to advise students not to become vegetarians and the cafeteria should not be allowed to offer meat-substitute foods."

Shifting the Burden of Proof

If we assert a statement as truth, it is up to us to establish its validity. We can't make the opponent of our argument responsible for proving its opposite (although we'd like to).

"Vegetarianism is a stupid, unnatural lifestyle, and I'd like to see anyone prove me wrong on that."

Stacking the Cards and

Slanting the Evidence

These two fallacies are similar in that they're brutishly unfair to the opposition. Stacking the cards means that we pile up the evidence on our side of the argument and cheat the other side of a fair representation. See the section on Anticipating the Opposition. Slanting the evidence means that we use words in our description of the opposition's argument that taint our readers' perception of the opposition before they even read it.

Another, more thorough, description of logical fallacies (with definitions and easy to understand examples) is Stephen Downes's Guide to the Logical Fallacies. Downes is an instructor, media design specialist, and webmaster at Assiniboine Community College in Brandon, Manitoba, Canada.

The other sub-sections of this part of Principles of Composition are as follows:

  • Citing Authorities
  • Using Personal Experience
  • Using Statistics
  • Using Facts
  • Using Analogies
  • Anticipating the Opposition
  • A Sample Essay (with commentary)
  • We recommend, also, the section on Logic, which is taken from the Purdue University Online Writing Lab. That material is more extensive — you'll find more fallacies — than what is presented here.