search

Become an active member of our fallacy-discussing community (or just become a lurker!)

Commutation of Conditionals

(also known as: the fallacy of the consequent, converting a conditional)

Description: Switching the antecedent and the consequent in a logical argument.

Logical Form:

If P then Q.

Therefore, if Q then P.

Example #1:

If I have a PhD, then I am smart.

Therefore, if I am smart, then I have a PhD.

Explanation: There are many who could, rightly so, disagree with the first premise, but assuming that premise is true, does not guarantee that the conclusion is true.  There are many smart people without PhDs.

Example #2:

If I have herpes, then I have a strange rash.

Therefore, if I have a strange rash, then I have herpes.

Explanation: I am glad this is not true.  One can have non-herpes rashes.

Exception: If p=q, then it is necessarily true that q=p.

Tip: If you think might herpes, see your doctor.

References:

Pickard, W. A., & Aristotle. (2006). On Sophistical Refutations. ReadHowYouWant.com, Limited.

Questions about this fallacy? Ask our community!

Master the "Rules of Reason" for Making and Evaluating Claims

Claims are constantly being made, many of which are confusing, ambiguous, too general to be of value, exaggerated, unfalsifiable, and suggest a dichotomy when no such dichotomy exists. Good critical thinking requires a thorough understanding of the claim before attempting to determine its veracity. Good communication requires the ability to make clear, precise, explicit claims, or “strong” claims. The rules of reason in this book provide the framework for obtaining this understanding and ability.

This book / online course is about the the eleven rules of reason for making and evaluating claims. Each covered in detail in the book. 

Take the Online Course