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BASIC CONCEPTS OF LOGIC & REASONING

# BASIC CONCEPTS OF LOGIC & REASONING - Introduction to...

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Introduction to Philosophy / Prof. Pruim’s Notes Basic Concepts of Logic and Reasoning / p. 1 BASIC CONCEPTS OF LOGIC & REASONING I. Good Arguments needs to be Valid, Sound, and Cogent. Argument, premises, conclusion. An argument is not just a series of statements. An argument attempts to prove that a certain statement is true. More specifically, an argument consists of a set of statements, called the premises , offered as reasons to regard another statement, the conclusion , to be true. A good argument proves the conclusion. That is, a good argument show s the audience that the conclusion is true. Here is an example. “Clinton was President <----a premise By law every President must be over 35 years old. <----a premise Therefore, Clinton is over 35.” <----the conclusion Defintions. To serve as a proof, the argument must be valid, sound, and cogent. Here are the definitions of these concepts. VALID =df.: If the premises were true, then the conclusion would necessarily also be true. SOUND =df.: The argument is valid, plus, the premises are indeed true. COGENT =df.: The audience knows that the premises are true. If an argument is sound, then its conclusion is true. If an argument is sound and cogent, then the audience comes to know that the conclusion is true

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Introduction to Philosophy / Prof. Pruim’s Notes Basic Concepts of Logic and Reasoning / p. 2 EXERCISES. Evaluate these arguments: “All Presidents are Republicans. Eisenhower was President. Therefore, Eisenhower was Republican.” VALID? Yes SOUND? No COGENT? No “Hilary Clinton will be the nominee of the Democrats in 2004. The Democratic nominee will win the Presidential election. Therefore, Hilary Clinton will win the Presidential election.” VALID? Yes SOUND? Do not know COGENT? No “All Presidents are over 35 years old. Bush is over 35 years old. Therefore, George Bush is President.” VALID? No SOUND? No, but the premises are true COGENT? Yes, premises are known to be true 3 PRINCIPLES If an argument is valid and its premises are true, then the conclusion is true. If an argument is valid and its conclusion is false, then at least one of the premises is false. If an argument is defective (by being invalid, or unsound, or not cogent), then the argument fails to show the conclusion to be true. QUESTION: “If an argument is defective (by being invalid, or unsound, or not cogent), then its conclusion is false .” Is that correct? -NO! Look at our example with Eisenhower.
Introduction to Philosophy / Prof. Pruim’s Notes Basic Concepts of Logic and Reasoning / p. 3 II. More about VALIDITY. To say that an argument is valid is to say that its conclusion would follow from its premises.

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