III. Some Basic Concepts of Logic Clarity  Definition -- lexical and stipulative -- ostensive -- definition by examples -- definition by a synonym -- genus and differentia genus = species differentia – has to be essential features. Examples  A mosque is a building, often with high towers and domes, where Muslims go to worship mosque  Yellow is a color that resembles a ripe lemon.  Yellow is the portion of the spectrum between green and orange.  Yellow is radiant energy with a wavelength of 580 nanometers.

 Extension (denotation) and intension (connotation) The extension of “chair” is this chair, that chair, … all the chairs that the word refers to. The intension of the word "chair" is (something like) "a piece of furniture designed to be sat upon by one person at a time." The intension of the word "chair" is (something like) "a piece of furniture designed to be sat upon by one person at a time." -- Thin and thick. – this chair, four-legged chair, furniture, physical object, thing, being. -- Thin and thick. – this chair, four-legged chair, furniture, physical object, thing, being. -- Related to universalism vs. holism. -- Related to universalism vs. holism.

Arguments and Validity  Arguments - not verbal fighting - not verbal fighting - basic structure - basic structure P premises P premises C conclusion C conclusion e.g. "I think she's in law school; she's always lugging around a pile of law books." - Sometimes the conclusion or some premises are omitted. - Sometimes the conclusion or some premises are omitted.

 Deductive Arguments and Validity - A (deductive) argument is valid if and only if it is impossible that simultaneously (a) all its premises are true and (b) its conclusion is false. - A (deductive) argument is valid if and only if it is impossible that simultaneously (a) all its premises are true and (b) its conclusion is false. - Not to be confused with truth value. - Not to be confused with truth value. - Propositions (e.g. premises and conclusions of arguments) are true or false. - Propositions (e.g. premises and conclusions of arguments) are true or false. - Arguments are never true or false; they can however be valid or invalid. - Arguments are never true or false; they can however be valid or invalid. - Many invalid arguments have true conclusions. - Many invalid arguments have true conclusions. Example: Some human beings are mortal, and Socrates is a human being. Therefore, Socrates is mortal. (Can you see why this is an invalid argument?) Example: Some human beings are mortal, and Socrates is a human being. Therefore, Socrates is mortal. (Can you see why this is an invalid argument?) - Many valid arguments have false conclusions. - Many valid arguments have false conclusions. Example: No human beings will ever die, and Socrates is a human being. Therefore, Socrates will never die. Example: No human beings will ever die, and Socrates is a human being. Therefore, Socrates will never die. - Every valid argument with a false conclusion has at least one false premise. - Every valid argument with a false conclusion has at least one false premise.

 Exercises P1 All bananas are purple. P2 All lettuce is orange. C All bananas and lettuce are either purple or orange. P1 All bananas are purple. P2 All lettuce is orange. C All bananas and lettuce are either purple or orange. P1 The Bible says God exists. C God exists. P1 The Bible says God exists. C God exists. P1 The Bible is the word of God. P2 The word of God is always true. P3 The Bible says that God exists. C God exists. P1 The Bible is the word of God. P2 The word of God is always true. P3 The Bible says that God exists. C God exists. P1 My parents have taught me that God does not exist. P2 Mom wouldn't lie. C God does not exist. P1 My parents have taught me that God does not exist. P2 Mom wouldn't lie. C God does not exist. War is the only way of stopping Saddam Hussein. After all, sanctions haven’t worked at all. War is the only way of stopping Saddam Hussein. After all, sanctions haven’t worked at all. Undemocratic societies kill the human spirit. The reason is clear: unless the people have the power in their society, the human spirit withers. Undemocratic societies kill the human spirit. The reason is clear: unless the people have the power in their society, the human spirit withers.

 Inductive reasoning Induction is a form of reasoning that makes generalizations based on individual instances. Induction is a form of reasoning that makes generalizations based on individual instances. P1 In the past, when I've gone home, my house has still been there. C When I go back home this afternoon, my house will still be there. P1 In the past, when I've gone home, my house has still been there. C When I go back home this afternoon, my house will still be there. P Every day to date the law of gravity has held. C. Therefore: The law of gravity will hold tomorrow. P Every day to date the law of gravity has held. C. Therefore: The law of gravity will hold tomorrow. - Statistic reasoning - Statistic reasoning e.g. This year x number of people will die in auto accidents in HK. e.g. This year x number of people will die in auto accidents in HK. - Causal reasoning - Causal reasoning e.g. Two weeks after they put fluoride in St. John’s water I got sick. I had a fever and couldn’t keep solid food down. So, I switched to drinking bottled water and I recovered in a day or so. That fluoridated water is dangerous stuff. e.g. Two weeks after they put fluoride in St. John’s water I got sick. I had a fever and couldn’t keep solid food down. So, I switched to drinking bottled water and I recovered in a day or so. That fluoridated water is dangerous stuff. - Arguments from Analogy - Arguments from Analogy e.g. Children are like flower, they need tender loving care. e.g. Children are like flower, they need tender loving care. - Arguments from authority - Arguments from authority

 Daily One-minute Paper 1. What is the big point you learned in class today? 1. What is the big point you learned in class today? 2. What is the main, unanswered question you leave class with today? 2. What is the main, unanswered question you leave class with today?