# Logic

## Using Informal Logic in the Tutoring Session

We've been talking about various ways of helping writers to structure their arguments so that they are clear, persuasive, and logical. What we haven't yet discussed are ways that you might use instruction in logic in the tutoring session to help a writer analyze her ideas.

What follows are some steps you might take in analyzing the logic of a paper:

1) Ask the writer if she's familiar with syllogisms. If not, explain to her that a syllogism consists of two premises - a major premise and a minor premise - and a conclusion. Here is one example:

• All men are mortal.
• Socrates is a man.
• Socrates is mortal.

Here is another:

• All women are brilliant.
• I am a woman.
• I am brilliant.

You'll want to take the opportunity to explain to the writer that an argument can be logical without being true (as in the second example).

2) Establish the argument's logic by breaking her argument down into its component syllogisms. Deductuve arguments rely on syllogisms in order to make sense. Go through the paper with the writer and try to find out what the he is really arguing by unearthing the syllogisms buried in her prose.

3) Establish the argument's truth by testing the validity of its premises. Consider, for example, the following syllogism:

• Murder is wrong.
• Abortion is murder.
• Abortion is wrong.

This argument may be logical, but is it true? If you accept the second premise - that "abortion is murder" - then you have no choice but to accept the conclusion drawn here. But is this second premise necessarily true? A writer will need to consider, in this case, the terms he is using. For example, murder is defined as "the unlawful killing of another human being with malice aforethought" (Random House Dictionary of the English Language). We have two problems applying this definition to abortion: first, abortion is legal, and second, we can debate whether or not a fetus is indeed a human being. Both matters must be addressed by the writer if he wishes to make an argument along the lines of the one suggested in the syllogism above.

4) Look for suppressed assumptions. Let's say that the writer of the abortion argument understood that a controversy exists as to whether a fetus can be considered a human being - and he neglected to expose what he knew. In this case, the writer is suppressing assumptions. Writers suppress assumptions all the time and for all kinds of reasons - some legitimate, some suspect. One legitimate reason for suppressing an assumption is that your readers can be counted on to agree with what you have to say. For example, if the writer of the abortion argument is writing a pamphlet for a Right to Life group, he will not need to prove that abortion is murder because it is an assumption that members of this group already share. Still, you will want to be on the lookout for suppressed assumptions, and to question writers as to why their argument wasn't more explicitly made.

5) Consider each premise and the evidence that supports it. Is that evidence adequate? Current? Reputable? If not, the reader will remain unconvinced of the validity of the premises, and the argument will fail.

## Avoiding Logical Fallacies

Logical fallacies are mistakes in reasoning. They may be intentional or unintentional, but in either case they undermine the strength of an argument. Some common fallacies are defined below. Please familiarize yourselves with them so that you can help writers to avoid them.

1) Hasty Generalization: A generalization based on too little evidence, or on evidence that is biased. Example: All men are testosterone-driven idiots. Or: After being in New York for a week, I can tell you: all New Yorkers are rude.

2) Either/Or Fallacy: Only two possibilities are presented when in fact several exist. Example: America: love it or leave it. Or: Shut down all nuclear power plants, or watch your children and grandchildren die from radiation poisoning.

3) Non Sequitur: The conclusion does not follow logically from the premise. Example: My teacher is pretty; I'll learn a lot from her. Or: George Bush was a war hero; he'll be willing to stand tough for America.

4) Ad Hominem: Arguing against the man instead of against the issue. Example: We can't elect him mayor. He cheats on his wife! Or: He doesn't really believe in the first amendment. He just wants to defend his right to see porno flicks.

5) Red Herring: Distracting the audience by drawing attention to an irrelevant issue. Example: How can he be expected to manage the company? Look at how he manages his wife! Or: Why worry about nuclear war when we're all going to die anyway?

6) Circular Reasoning: Asserting a point that has just been made. Sometimes called "begging the question." Example: She is ignorant because she was never educated. Or: We sin because we're sinners.

7) False Analogy: Wrongly assuming that because two things are alike in some ways, they must be alike in all ways. Example: An old grandmother's advice to her granddaughter, who is contemplating living with her boyfriend: "Why should he buy the cow when he can get the milk for free?"

8) Post Hoc, Ergo Propter Hoc: The mistake of assuming that, because event a is followed by event b, event a caused event b. Example: It rained today because I washed my car. Or: The stock market fell because the Japanese are considering implementing an import tax.

9) Equivocation: Equates two meanings of the same word falsely. Example: The end of a thing is its perfection; hence, death is the perfection of life. (The argument is fallacious because there are two different definitions of the word "end" involved in the argument.)

Written by Karen Gocsik