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Logic and Reasoning Panther Prep North Central High School.

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Presentation on theme: "Logic and Reasoning Panther Prep North Central High School."— Presentation transcript:

1 Logic and Reasoning Panther Prep North Central High School

2 Logical Proof Logical reasoning is the easiest way to convince because the information is presented as fact. However, not all information is common sense to the audience so the speaker has to connect the dots. To do this, the speaker can use: –Deductive reasoning –Inductive reasoning

3 Introduction Logic –the study of reasoning –allows us to test the truth or falsity of inferences and reasoning –used in problem solving

4 Inference …reaching a conclusion on the basis of evidence and reasoning –the creation of new ideas or information from existing ideas or information –the process of creating new statements from other statements these statements are called Propositions Propositional Logic—the logic of propositions—analyzing the validity of propositions

5 Induction Inductive reasoning –the inference of a general law from particular instances –the process of summarizing observations to derive a generalization about the world –we rarely observe all of the instances if a particular phenomena, so we can never be sure it is true in all cases—we can estimate probability

6 Induction A daisy is a flower. A rose is a flower. A violet is a flower. Therefore, plants with colorful blooms are flowers.

7 Deduction Deductive reasoning is a way for the speaker to draw a direct line from a general concept to the specific end of their purpose. …the inference of particular instances by reference to a general law or principle Sherlock Holmes’ deductive reasoning techniques The format for these sets is called a syllogism

8 Syllogisms All men are mortal. Socrates is a man. Therefore, Socrates is mortal. –The 1 st statement is the generalization or general rule called the major premise –The 2 nd statement is an observation or specific fact called the minor premise –The 3 rd statement is the inference that follows the first two statements called the conclusion

9 Validity and Truth The Rules of Inference tell us whether a syllogism is valid or not, but not if it is true. –Validity is simply a matter of correct reasoning. To determine if a conclusion of a valid syllogism is true, we have to agree that the premises are true. –When a syllogism is both valid in reasoning and the premises are true, we say the conclusion is sound.

10 Accuracy vs. Precision Accuracy: proximity to target or true value Precision: proximity to similar situations Accurate, but not precise Precise, but not accurate

11 Fallacies Fallacies are mistruths that are used to make a point. Fallacies are generally used to dramatize a position, dramatize information or to compensate for the lack of supporting information. While popularly used, they can lead to a destruction of the credibility of the speaker and therefore a destruction of the speech itself.

12 Types of Fallacies Types of fallacies include: –Unwarranted or Hasty Generalization (Including information that does not apply.) –Errors in casual information Post Hoc – Unproven cause-effect relationship Non Sequitur – Stating a conclusion that does not necessarily follow the argument. –Begging the Question (States as fact what needs to be proven.) –Ignoring the Question (Misdirection of attitude)

13 Types of Fallacies (Cont.) Types of fallacies include: –False Analogy (A parallel that does not exist.) –Either/Or Fallacy (Stating only two options when more exist.) –Ad Hominem (Attack of character on the opposition) –Red Herring (Addition of information to confuse) –Ad Populum (Public opinion MUST be right, right?)

14 Identifying Fallacies See if you can determine what, if any, fallacy is present in the following statements: –“The Ford Explorer is the most popular SUV on the market, so it must be the safest.” –“You were the only person working when the accident happened so it must be your fault.” –“If you don’t finish this paper, you will become a bum and live in a van down by the river.” –“The rate of crime is increasing in our schools because of the reduction of art and music programs.”

15 Identifying Fallacies (Cont.) –“If you do not vote for the private school funding bill you simply do not care about children.” –“Stand back! I can help. My dad is a doctor.” –“Johnny is not fit to lead this project because he can’t even tie his shoes in the morning.” –“Mom, if you don’t buy me an iPhone, it means that you don’t really love me.” –“Would we not work harder if we made more money?” –“You either finish the project tonight or you will get eaten by a werewolf.”

16 Validity and Truth Validity does not guarantee truth and truth does not guarantee validity. In order to have a sound syllogism, the form must be valid and the premises must be true.

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