Introduction to Formal Fallacies

Errors in Reasoning Due to Bad Logic

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NOTE: This course is included in the site-wide bundle which unlocks every course in the Academy.


This course introduces some of the most common argument forms that use premises of the form “A or B”, “If A then B”, “All A are B” and “Some A are B”, and the most common logical fallacies that result from improper reasoning based on these claims.

These argument forms have been studied and taught for centuries. They were a basic component of the liberal arts curriculum of the Medieval university system. Hence the use of Latin names like “modus ponens” and "modus tollens" to identify specific fallacies.

Our goal as critical thinkers should be to recognize these argument forms when they appear in ordinary language, and understand why they are valid and invalid.

What Will I Learn in This Course?

In this course you'll learn:

  • How to identify and analyze the most common valid and invalid argument forms that are based on the logic of conjunctions ("A and B"), disjunctions ("A or B"), conditional claims ("If A then B"), and generalizations ("All A are B"; "Some A are B")
  • The invalid forms of these arguments are known as "formal fallacies" or "structural fallacies".

What Do I Get With This Course?

This a short course, but it covers important topics that are taught in every critical thinking and logic text.

  • 9 video lectures, totaling just under 30 minutes of viewing time
  • Full transcripts for each of the lectures, embedded below the videos
  • Discussion comments for each of the lectures, allowing you to ask and respond to questions and comments
  • a pdf ebook, suitable for printing or viewing on a desktop computer or tablet device
  • quiz questions to help you review and test your knowledge

The logical properties of conjunctions, disjunctions and conditional claims are introduced and discussed in the “All the Formal Logic You Need to Know For Critical Thinking” course. It's not necessary to have access to those tutorials in order to follow this course, but that course will certainly deepen your understanding of formal fallacies, and the logical properties of natural language in general.

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