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Lecture 5_Argument forms; proving invalidity

# Lecture 5_Argument forms; proving invalidity - Lecture 5...

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Lecture 5 Argument Forms; Proving Invalidity Patrick Maher Philosophy 102 Spring 2009

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Alternative notation So far, when putting arguments in logical form, we have written ‘therefore’ to indicate the conclusion. Example All men are mortal. Socrates is a man. Therefore, Socrates is mortal. An alternative notation is to draw a line above the conclusion and omit the word ‘therefore’. Example All men are mortal. Socrates is a man. Socrates is mortal.
Argument form Definition An argument form is an arrangement of words and letters such that the uniform substitution of terms or statements in place of the letters results in an argument. Example All A are B . All B are C . All A are C . Substituting A = salmon, B = fish, C = animals, results in: All salmon are fish. All fish are animals. All salmon are animals.

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Example If A then B . A . B . If we substitute: A = there are dried-up riverbeds on Mars B = water once flowed on the Martian surface then we get this argument: If there are dried-up riverbeds on Mars then water once flowed on the Martian surface.
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Lecture 5_Argument forms; proving invalidity - Lecture 5...

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