Logic 11-13

# Logic 11-13 - Logic Presentation November 13, 2007 Review:...

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Logic Presentation Logic Presentation November 13, 2007 November 13, 2007

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Review: Statements Review: Statements A statement is a complete thought capable of being true or false. Statements are expressed by sentences. A simple statement is one and only one complete thought. Examples: John is tired. Students aren’t lazy A compound statement is composed of more than one complete thought. Examples: Students aren’t lazy but Bob is. Kate is wakeful or John is wakeful. If Kate is studying logic, then John is studying logic.
Our Plan Our Plan In focusing on Categorical Syllogisms, we worked with deductive arguments each premise of which was a simple statement. This week, we’ll focus on deductive arguments that have compound statements among their premises. After that, we’ll turn to fallacies and inductive arguments.

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Review: Distinction between Inductive and Review: Distinction between Inductive and Deductive Arguments Deductive Arguments An argument is deductive if and only if its proponent maintains that it is impossible for its premises to be true and its conclusion false. An argument is inductive if and only if its proponent maintains that the truth of its premises makes its conclusion likely (though not absolutely certain ).
Deductive Arguments: Review Deductive Arguments: Review Validity: A deductive argument is valid if and only if it is impossible for its premises to be true and its conclusion false. Invalidity: A deductive argument is invalid if and only if it is possible for its premises to be true and its conclusion false. Soundness: A deductive argument is sound if and only if (a) it is valid and (b) all of its premises are true.

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Validity: Review Validity: Review An argument is valid if and only if it is impossible for the argument’s premises to be true and its conclusion false. So, given any valid argument, this sort of situation: 1. Premise 1 2. Premise 2 n. Premise n Conclusion is absolutely impossible . True False
Validity: Review Validity: Review What makes a valid argument valid? What is it about a valid argument that makes it the case that it is impossible for its premises to be true and its conclusion false? Almost always, it is a valid argument’s form that makes it valid.

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Validity: Review Validity: Review In all but some exceptional sorts of cases, when one encounters a valid argument, the argument is valid because it has a certain form . Such an argument is called a “formally valid argument.” A formally valid argument is valid in virtue of its argumentative structure ; it is valid in virtue of the pattern of reasoning it employs. So, a (formally) valid argument is valid because it has a certain form. Given a (formally) valid argument, any argument having the same form is also valid.
Extracting the Form of an Argument Extracting the Form of an Argument We know that we can extract an argument’s form by employing letters to stand for “chunks of content”; the same “chunk of content” is assigned the same letter throughout the

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## This note was uploaded on 04/07/2008 for the course PHIL 115 taught by Professor Stoltz during the Fall '07 term at St. Thomas.

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Logic 11-13 - Logic Presentation November 13, 2007 Review:...

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