What are Copi's 18 Core Fallacies?

Update #2: I now have a copy of the third edition of Irving M. Copi's "Introduction to Logic."

You'll recall that there are currently 15 editions of this book and that in the 14th edition, there are 19 logical fallacies:

• 7 fallacies of relevance (the appeal to the populace, the appeal to emotion, the red herring, the straw man, the attack on the person, the appeal to force and missing the point/irrelevant conclusion)


• 4 fallacies of defective induction (the argument from ignorance, the appeal to inappropriate authority, false cause, hasty generalization)


• 3 fallacies of presumption (accident, complex question, begging the question)


• 5 fallacies of ambiguity (equivocation, amphiboly, accent, composition, division)

In the much earlier third edition, there are 18 fallacies:

• 13 fallacies of relevance (the appeal to force, the attack on the person-abusive, the attack on the person-circumstantial, the argument from ignorance, the appeal to pity, the appeal to the populace, the appeal to authority, accident, hasty generalization, false cause, begging the question, complex question, irrelevant conclusion)


• 5 fallacies of ambiguity (equivocation, amphiboly, accent, composition, division)

Comparing the two, it seems several of the "fallacies of relevance" were later broken out into two separate categories: "fallacies of defective induction" and "fallacies of presumption." In addition:

1. The attack on the person (ad hominem) was collapsed into one fallacy in later editions (-1=17)


2. The red herring was added (+1=18)


3. The straw man was added (+1=19)

And that is how "18 core fallacies" became 19. Not sure why online lists reference 15. Perhaps that is the count in yet another edition!

Wow. I hadn’t heard of this book, either, but color me impressed!

”For more than six decades, and for thousands of students, Introduction to Logic has been the gold standard in introductory logic texts ...

“Irving M. Copi was a logician who studied under Bertrand Russell while at the University of Chicago. He held appointments at, among other institutions, Princeton University, the University of Michigan, and the University of Hawaii at Manoa ...”

This book is now in at least its 15th edition, which may explain why the number of fallacies has changed. Over time, the author/editors probably combined certain fallacies into one fallacy.

FYI, there are affordable, used editions of this book online that sell for under $10. I’m going to grab a third edition that looks to be in pretty good shape for $25. Thanks for the tip. I love interesting old books!

Update: According to the 14th edition of Irving M. Copi's "Introduction to Logic," which I now own in PDF form, there are 19 logical fallacies:

• 7 fallacies of relevance (the appeal to the populace, the appeal to emotion, the red herring, the straw man, the attack on the person, the appeal to force and missing the point/irrelevant conclusion)


• 4 fallacies of defective induction (the argument from ignorance, the appeal to inappropriate authority, false cause, hasty generalization)


• 3 fallacies of presumption (accident, complex question, begging the question)


• 5 fallacies of ambiguity (equivocation, amphiboly, accent, composition, division)

I suspect earlier editions had 18 (or later editions since I have seen a 15th edition book cover), and earlier editions had 15. That's the cause of the confusion.

Soon I will own a used hardcover of the 3rd edition and will report back to you what I find.