Summary from Purdue’s Online Writing Lab:This resource covers using logic within writing-- logical vocabulary,logical fallacies, and other types of logos-based reasoning.Contributors:Ryan Weber, Allen BrizeeLast Edited: 2011-06-28 02:07:33Website: http://owl.english.purdue.edu/owl/resource/659/1/
What is logic? • Logic is a method of reasoning that helps prove arguments. •Logic works by assessing the accuracy of a collection of statements. • To be deemed logical, testing of such accuracy should occur in a sequence.
What is logic? This logical sequence, or syllogism, comes from the Greek philosopher Aristotle: Premise 1: All men are mortal. Premise 2: Socrates is a man. Conclusion: Therefore, Socrates is mortal. Note that if Premise 1 is accurate, and Premise 2 is accurate, a logical conclusion is derived from both statements.
Logical Vocabulary Before using logic to reach conclusions, it is helpful to know some important vocabulary related to logic. Premise: Proposition used as evidence in an argument. Conclusion: Logical result of the relationship between the premises. Conclusions serve as the thesis of the argument. Argument: The assertion of a conclusion based on logical premises. Syllogism: The simplest sequence of logical premises and conclusions, devised by Aristotle. Enthymeme: A shortened syllogism which omits the first premise, allowing the audience to fill it in. For example, "Socrates is mortal because he is a human" is an enthymeme which leaves out the premise "All humans are mortal." Induction: A process through which the premises provide some basis for the conclusion. Deduction: A process through which the premises provide conclusive proof for the conclusion. From “Using Logic”, Purdue OWL
Reaching Logical Conclusions The goal of using syllogisms is to use premises to arrive at only one logical conclusion. Example: Premise 1: Maria loves sugar. Premise 2: Most pastries at the Flying M Coffee Garage contain sugar. Conclusion: Maria loves the pastries at Flying M Coffee Garage.
Reaching Logical Conclusions • More than 2 premises may be needed to come to a conclusion. • Logic allows specific conclusions to be drawn from general premises. • Logic will not work if the reader does not accept one or more of the author’s premises. • From OWL: “Different premises could lead to very different conclusions about the same subject. For instance, these two syllogisms about the platypus reveal the limits of logic for handling ambiguous cases: Premise 1: All birds lay eggs. Premise 2: Platypuses lay eggs. Conclusion: Platypuses are birds. Premise 1: All mammals have fur. Premise 2: Platypuses have fur. Conclusion: Platypuses are mammals. Though logic is a very powerful argumentative tool and is far preferable to a disorganized argument, logic does have limitations. It must also be effectively developed from a syllogism into a written piece.”
Logical FallaciesNot surprisingly, there are many logical fallacies. Here are some of them to look for and avoid:Slippery Slope: A conclusion based on the premise that if A happens, and B, C,D… all the way down the line to Z happens, then A equates to Z.Hasty Generalization: This happens when a writer jumps to a conclusion based oninsufficient or biased evidence.Post hoc ergo propter hoc: Assumes that if A occurred after B then B musthave caused A. Genetic Fallacy: The conclusion draws from the idea that origins of a determine character, nature, or worth. Begging the Claim: The conclusion that the writer should prove is contained and validated within the claim. Example: Filthy and polluting coal should be banned.
Logical FallaciesCircular Argument: An argument is restated within the conclusion instead of proving it.Either/or: This is a conclusion that oversimplifies the argument by reducing it to only two sidesor choices. Example: You can either eat my cooking or starve to death.Ad hominem: This is an attack on the character of a person rather than her/his opinions orarguments. Example: Occupy Boise and camps like it are full of homeless thugs.Ad populum: An emotional appeal that speaks to positive or negative concepts rather thanthe real issue at hand. Example: If you were a true blue CWI student you would vote in favorof the unicorn as school mascot. Red Herring: This is a diversionary tactic that avoids the key issues, often by avoiding opposing arguments rather than addressing them. Straw Man: This move oversimplifies an opponents viewpoint and then attacks that hollow argument. Example: People who support the Tea Party movement want to go back to the days of slavery. Moral Equivalence: This fallacy compares minor misdeeds with major atrocities.
Using Logic in Writing From OWL: When converting logical syllogisms into written arguments, remember to: • Lay out each premise clearly • Provide evidence for each premise • Draw a clear connection to the conclusion.
Works Cited “Purdue OWL: Using Logic." Welcome to the Purdue University Online Writing Lab (OWL). Web. 9 Dec. 2011.