{ Introduction to Logic The two types of logos

Induction  Definition: compiling of evidence/reasons/ examples that support an argument  Example: “Wow! My dog smells terrible! She was outside all night, and around midnight I smelled skunk at the back of the house. I heard her barking loudly, too. That’s definitely a skunky smell on her. She must have tangled with that skunk.”

Deduction  Definition: deductive logic is built on premises, or statements upon which all parties agree, which, when considered logically, lead to a strong conclusion  Example: syllogism (formal statement of deductive proof)  Major premise: All humans are mortal.  Minor premise: Socrates is human.  Conclusion: Socrates is mortal.

 Syllogisms are rarely found in their simplest form.  Instead, they often appear as enthymemes.  Simply put, an enthymeme is a claim supported by a reason expressed as a because clause. Syllogisms

 “I hear you and Elizabeth are getting married.” “Yes, that’s true.” “Well, now that you’ve got a woman to cook for you, maybe you could invite me over for dinner sometime.” “Why do you think Elizabeth will be doing the cooking?” “Because she’s a woman.” Turn this enthymeme into a syllogism. Enthymeme example

{{ Premise: Women do all the cooking in a family. Premise: Elizabeth is a woman. Conclusion: Elizabeth will do all the cooking. (And presumably, her husband will be eating better meals, so his friend wants to be invited over.) Enthymeme to syllogism

 “I’d better close the windows because the sky is getting darker.” What is the major premise, minor premise and conclusion contained in this statement? Enthymeme example

Enthymeme to syllogism  Major premise: Dark skies mean it will rain.  Minor premise: The sky is getting darker.  Conclusion: It will rain. (And presumably, I don’t want wet carpet, so I will close the windows.)

 1. He must be happy because he’s smiling all the time.  2. A nuclear war is inevitable, for our sworn enemy, North Korea, has a hydrogen bomb.  3. He would not take the crown. Therefore, ‘tis certain he was not ambitious. (Julius Caesar)  4. Since you didn’t speak up in my defense at the meeting, you must be as much against me as the rest of them are. Enthymeme practice

 Thomas Jefferson, primary author of the Declaration of Independence, was an educated man well schooled in logic.  The Declaration is an extended enthymeme (it contains premises that lead to a logical conclusion).  After reading the Declaration of Independence, work with your group to write the syllogism that is the basic idea behind the document.  Remember to write it in the form of premise- premise-conclusion. Test on syllogisms