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LOGIC AND CRITICAL THINKING The Way to the Good Reasoning and Making Good Argument 時間:92年10月18日 地點:東吳大學外雙溪 主講:米建國 東吳大學哲學系 What Is Critical Thinking? Think it twice: Don’t take things for granted so easily. Always ask the why-question: Try to find out the reason (the premises) why certain claim (the conclusion) can be supported. Examine and evaluate the relationship between the reasons and the claim. Paradoxes Self-defeating paradox: The concept of “all powerful” God Zeno’s paradox: An apparently unacceptable conclusion derived by apparently acceptable reasoning from apparently acceptable premises Semantic paradox: The liar’s paradox The lawyer’s paradox Prisoner’s dilemma Russell’s paradox (Barber’s paradox) The lottery paradox What is logic? Logic is not an empirical science Formal or informal science Logic v.s.Psychology: 1. The Laws of Thinking 2. The Science of Reasoning 3. The Science of Argument The study of the methods and principles used to distinguish good (correct) from bad (incorrect) reasoning or argument. The way to the good reasoning (making good argument) and critical thinking What Is an Argument? An argument is the fundamental structure of the reasoning. An argument consists of premises and conclusion. An argument is used to provide reasons for supporting some claim or proposal. Logic aims to the study of the various forms of argument. The ultimate goal of logic is to evaluate arguments. The Standard Form of Argument P = premise, C = conclusion There must be some kind of supporting relationship between premises and conclusion. P1 P2 、 、 Pn (n≧1) C Two Kinds of Argument The traditional but mistaken distinction between deduction and induction: Deduction Some general principles ↓ A particular case Induction Some particular cases ↓ A general principle Deductive Argument Deductive argument is the argument that the premises necessarily support the conclusion. P1 P2 、 、 Pn C Inductive Argument Inductive argument is the argument that the premises probably support the conclusion. P1 P2 、 、 Pn C Evaluating An Argument There are two ways of evaluating an argument. Formal logic is to use the deductive criterion for evaluating arguments. Informal logic is to use the inductive criterion for evaluating argument. The Criterion for Evaluating a Deductive Argument Deductive Argument Valid Arg. Sound Arg. Unsound Arg. Good Arg. Bad Arg Invalid Arg. Unsound Arg. Bad Arg. The Criterion for Evaluating an Inductive Argument Inductive Argument Strong Arg. Cogent Arg. Good Arg. Uncogent Arg. Bad Arg. Weak Arg. Uncogent Arg. Bad Arg. What Is a Good Argument Deductive Valid Sound Good Inductive Invalid Unsound Bad Unsound Bad Strong Cogent Good Weak Uncogent Bad Uncogent Bad The Deductive Systems The truth table methods for evaluating deductive arguments The formal system of natural deduction: 1. Propositional logic 2. Predicate logic The Aristotelian logic (Categorical Syllogism) The axiomatic system The Inductive Systems The methods of analogy and the probable inference Legal reasoning Mill’s method and causality Statistical reasoning and probability Hypothetical reasoning Informal Fallacies A fallacy is an error in reasoning. Fallacies of relevance: When an argument relies upon premises that are not relevant to its conclusion, and therefore cannot possibly establish its truth Fallacies of weak induction: When the connection between premises and conclusion is not strong enough to support the reasoning Fallacies of presumption, ambiguity, and grammatical analogy The Uses of Logic Evaluate someone else’s argument by exposing its structure Set up your own argument Solve problems and puzzles by answering the whyquestions (giving the reasons) Inference to the best through using the present evidences Thinking effectively and making decision wisely Logic and Critical Thinking Why should we become a critical thinker? Be the master of your own life To ask “why?” is to ask for the reasons for some beliefs and opinions (that is, to find out the premises for a certain conclusion) To evaluate how the reasons successfully support the claim (that is, to evaluate how the premises support the conclusion ) A critical thinker is a truth-pursuer, and logic is truthpreserving. The End!