PHIL102 Ch1notes - PHILOSOPHY 102 Chapter 1 LOGIC?...

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PHILOSOPHY 102 INTRODUCTION TO LOGIC Chapter 1 Basic Concepts LOGIC? Psychology vs. Logic -We are not interested in how people actually think, reason, and make inferences. (These are psychological facts about humans.) -We are interested in how people ought to make inferences. (These involve logical facts about the contents of statements.) BASIC CONCEPTS The central concept: an ARGUMENT —a set of statements, some of which are the reasons (or “premises”), used to establish another statement (or “conclusion”). Note: a statement is an item of language that is used to make an assertion, i.e., a declarative sentence. It is something that is either true or false . Truth and falsity are features of statements that we may call truth - values . Compare kinds of sentences: 1. Logic is amazing! (Exclamation) 2. Don’t stop the music. (Command) 3. Where has everyone gone? (Question) 4. There are four kinds of sentences. (Assertion) We are interested in declarative sentences or assertions. 2 basic principles about statements: 1. Every statement is either true or false. (“Law of Excluded Middle”) 2. No statement is both true and false. (“Principle of Non-Contradiction”) [Philosophical aside: a leading view on the nature of truth is The Correspondence Theory of Truth . This holds that a statement is true just when it corresponds to the way the world is and false just when it does not. (What is the “correspondence” relation?).] The premises and conclusion of an argument are statements. They are things that are either true or false. (This will be important in chapter 7.)
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Let’s say (p.3): “LOGIC is the study of methods for evaluating whether the premises of an argument adequately support (or provide good evidence for) its conclusion.” Examples of arguments: A. All men are mortal. Socrates is a man. So, Socrates is mortal. B. Taco is a collie. No collies are cats. So, Taco is not a cat. C. If you love me you will make me pancakes for breakfast, but since you don’t love me, I guess I am not getting any pancakes. D. Since 1 > 2 and 2 > 4 and 4 > 10, it follows that 1 > 10. Notice: Arguments A and B are good ones, but C and D are not good. SECTION 1.1 Validity and Soundness Validity -The strongest way for a set of premises to support a conclusion is for the argument they comprise to be VALID. (Note: this is a technical meaning of ‘valid’, not the common meaning of “relevant” or “reasonable”) An argument is valid just when it is necessary that if the premises are all true, then the conclusion is also true. (p.3-6) (Alternatively: an argument is valid just when it is impossible for the premises to be true and the conclusion false.) Notice: the characterization of validity does not require that the premises actually be true for the argument to be valid, only that IF they were true then the conclusion would also be true. The relation expressed by the notion of validity is that of entailment between a set of statements and another statement. This is a relation between the contents of
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This note was uploaded on 05/01/2008 for the course PHIL 102 taught by Professor Epperson during the Fall '07 term at Western Washington.

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PHIL102 Ch1notes - PHILOSOPHY 102 Chapter 1 LOGIC?...

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