Chapter 5: Formal and Informal Logic
Chapter 5: Formal and Informal Logic
Chapter 5: Formal and Informal Logic
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The Paradox of the Liar<br />
Is the following proposition true or false?<br />
This proposition is false<br />
• If every proposition is either true or false then this proposition will<br />
be either true or false<br />
• If it is true, then it is true that it is false; so it must be both true <strong>and</strong><br />
false<br />
• If it is false, then it is false that it is false; so it must be true; so it<br />
must be both true <strong>and</strong> false<br />
• So in both cases it is both true <strong>and</strong> false, which is impossible<br />
ARGUMENT: Critical Thinking, <strong>Logic</strong> <strong>and</strong> the Fallacies <strong>Chapter</strong> 5: <strong>Formal</strong> <strong>and</strong> <strong>Informal</strong> <strong>Logic</strong> 5–14
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