Critical Thinking and Logical Arguments This lecture will discuss some of the bases and uses of logical arguments. It should be noted that logical argumentation is used only infrequently; indeed, there are times in which it might be neither appreciated nor appropriate. “This building is burning down. Thus, there is fire in this building. Your skin probably does not react well to contact with fire. In fact, contact with fire will prove both painful and injurious to you. Therefore, you should get out of the building.” As we know, there are many situations in which persuasion is more useful than logic. Our twin goals for this class are: 1. 2. To develop logical argumentation as a tool, and To understand when it should be used and when avoided. Standard Arguments and Logical Arguments The common definition of “argument” involves a loud shouting match. Logical argumentation is the process whereby a conclusion is drawn from one or more premises. The process of a logical argument differs from that of a confrontation in that: 1) 2) It distinguishes facts from opinions and plausible inferences, If attempts to focus on essentials, omitting issues that are tangential. Pure logical argumentation is a structural process, independent of consequences. Real life is seldom without consequences. Consider a lawyer presenting a logical argument for the acquittal of her client. Here the consequences are jail time or worse. Conclusions: 1. 2. Arguments in real life ideally are structured on the formal model, but often diverge from that model. We need to be able to understand the difference between argumentation based on critical thinking and that based on consequences, and use both. Logical Fallacies 1. Ad hominem Attack the person making the argument, rather than the logic of the argument itself. “My opponent is a sexagenarian and a thespian.” Also called the “domino effect”. If Vietnam falls, so will all of Southeast Asia. This famous person believes this, so you should also. “Post Hoc, Ergo Propter Hoc” “After this, therefore because of this”. Columbus discovered the Americas in 1492. As a result, tobacco was introduced into Europe. Average lifespan in Europe has increased greatly since 1492. Therefore, smoking tobacco is good for you. Assuming the conclusion. “I am not a criminal, so nothing I do is illegal.” 2. Slippery Slope 3. Appeal to Authority 4. False Cause 5. Begging the question More Logical Fallacies 6. Fallacy of Composition 7. Ambiguity of premises Assuming the whole has characteristics of a part. Some Sicilians are Mafioso, so all Sicilians are. Use of words with ambiguous meaning in stating the premises of an argument. God is love, Love is blind, Ray Charles is blind, Therefore, God plays the piano.* I do not want to believe this, so it is not true. 8. Ethical Egoism *Logical Form: Four elements a, b, c, d and one set S. a=b b=c d=c d S (implied argument from assumed knowledge of Mr. Charles), so a S. Problem: Multiple uses of the word “is” and ambiguous use of the word “blind”. Valid and Invalid Arguments Claims are true or false. Arguments are valid or invalid. The term “validity” means that the conclusion of the argument necessarily follows from the premises, assuming the truth of the premises. Valid arguments are called “sound” if they are based on true premises, otherwise they might be “unsound”. Note that the conclusion of an invalid or unsound argument is not necessarily false, it just cannot be guaranteed to be true. Deductive and Inductive Argumentation Classical argumentation is deductive; it proceed from true premises through valid argumentation into the production of new facts. Inductive argumentation proceeds from evidence to plausible conclusions. Even though inductive arguments might not be valid, they can be strong if based on sufficient evidence.