SYLLOGISM FORM LOGICAL REASONING WHAT IS A SYLLOGISM

SYLLOGISM - FORM & LOGICAL REASONING

WHAT IS A SYLLOGISM? • Syllogism – the formal structure of logical argument. • Three statements - Major Premise, Minor Premise, and Conclusion. • Major Premise – general statement, assumed true. • Minor Premise – specific statement, assumed true • Leading to a logical conclusion based on the premises.

THREE TYPES OF SYLLOGISMS • What structures / forms of reasoning are true? • Three different kinds of syllogism: 1. Categorical 2. Conditional 3. Disjunctive

THREE TYPES OF SYLLOGISMS • What structures / forms of reasoning are true? • Three different kinds of syllogism: 1. Categorical – (all / every) 2. Conditional – (if / then) 3. Disjunctive – (either / or) Based on different premises in the assumption.

CATEGORICAL (ALL / EVERY) • Something true about all members of a category must be true about a particular example. • Expressed using variables: Major: A is true about B. Minor: C is equivalent to B. Conclusion: A is also true about C. • Example: Major: All men are mortal. Minor: Socrates is a man. Conclusion: Therefore, Socrates must be a mortal.

PRACTICE: • Finish the Categorical Syllogism: Major: All dogs go to heaven. Minor: ___________________. Conclusion: Therefore, ___________.

CONDITIONAL (IF / THEN) • If a first assumption proves to be true, then a logically related assumption must also be true. • Expressed using variables: Major: If A is true, then B is true as well. Minor: A is true. Conclusion: B must be true as well. • Example: Major: Where there’s smoke, there’s fire. Minor: There is smoke. Conclusion: Therefore, there must be a fire.

PRACTICE: • Finish the Conditional Syllogism: Major: If I am late to work, I’ll get in trouble. Minor: ___________________. Conclusion: Therefore, ___________.

DISJUNCTIVE (EITHER / OR) • If a first assumption proves to be true, then a related but contradictory assumption must be false. • Expressed using variables: Major: If A is true, then B must be false. Minor: A is true. Conclusion: B must be false then. • Example: Major: Either I pay more taxes, or get audited by the IRS. Minor: I did pay my taxes. Conclusion: Therefore, I won’t be audited by the IRS.

PRACTICE: • Finish the Disjunctive Syllogism: Major: Either I spend the whole weekend playing video games, or I do some studying. Minor: ___________________. Conclusion: Therefore, ___________.

ABBREVIATED SYLLOGISMS • When people speak, they don’t articulate the full logical structure of their reasoning. • Mr. Burtosky might say: “The substitute is a teacher, so give her the same respect while I’m gone. • The logic underlying this statement is: Major: You should respect your teachers. Minor: The substitute is a teacher. Conclusion: You should respect her too. • What statement was left out in what Mr. Burtosky said?

ENTHYMEME • Enthymeme – an abbreviated syllogism, where one of the premises making up a logical deduction is left unstated. • Etymology – Enthymeme is Greek for “in-the-mind”. • The missing premise is inferred by the audience listening to the argument.

CONVERTING ENTHYMEMES - EXAMPLE • If I say “Max is originally from Canada, so he really likes maple syrup. ” Major Premise: All Canadians like maple syrup. Minor Premise: Max is a Canadian. Conclusion: Therefore, Max likes maple syrup. • If I say “The only thing that matters is the number of games, that’s why the PS 4 is best console. ” Major Premise: The console with the most games is the best. Minor Premise: The PS 4 has more games than any other console. Conclusion: Therefore, the PS 4 is the best console.

CONVERTING ENTHYMEMES - PRACTICE • Jace is on the speech and debate team, so he must be good at public speaking. ” Major Premise: _____________________. Minor Premise: _____________________. Conclusion: Therefore, _________________. • We should go to fast food place with the best breakfast, which means we should go to Jack in the Box. ” Major Premise: _____________________.

CONCLUSION • A syllogism is the formal structure of logical argument. • Made up of three parts, a major premise, minor premise, and conclusion. • Three kinds of syllogisms, categorical (every / all), conditional (if / then), and disjunctive (either / or). • An enthymeme is an abbreviated syllogism, with one premise unstated and assumed by the audience.

ASSIGNMENT INSTRUCTIONS • To demonstrate your knowledge of logical reasoning, you will identify and analyze the ENTHYMEME (abbreviated argument) being communicated by a magazine advertisement: • Select a magazine advertisement. • Cut it out, and tape / glue it to a piece of notebook paper. • Summarize the advertisement’s message (complete sentence). • Re-write that message as a syllogism (major, minor, conclusion). • Identify which premise was left unstated - the inference.