Accused of a fallacy? Suspect a fallacy? Ask Dr. Bo and the community!

Quickly register to comment, ask and respond to questions, and get FREE access to our passive online course on cognitive biases!

one moment please...

Ambiguity Fallacy

(also known as: ambiguous assertion, amphiboly, amphibology, semantical ambiguity, vagueness)

Description: When an unclear phrase with multiple definitions is used within the argument; therefore, does not support the conclusion.  Some will say single words count for the ambiguity fallacy, which is really a specific form of a fallacy known as equivocation.

Logical Form:

Claim X is made.

Y is concluded based on an ambiguous understanding of X.

Example #1:

It is said that we have a good understanding of our universe.  Therefore, we know exactly how it began and exactly when.

Explanation: The ambiguity here is what exactly “good understanding” means.  The conclusion assumes a much better understanding than is suggested in the premise; therefore, we have the ambiguity fallacy.

Example #2:

All living beings come from other living beings.  Therefore, the first forms of life must have come from a living being.  That living being is God.

Explanation: This argument is guilty of two cases of ambiguity.  First, the first use of the phrase, “come from”, refers to reproduction, whereas the second use refers to origin.  The fact that we know quite a bit about reproduction is irrelevant when considering origin.  Second, the first use of, “living being”, refers to an empirically verifiable, biological, living organism.  The second use of, “living being”, refers to a belief in an immaterial god.  As you can see, when a term such as, “living being”, describes a Dodo bird as well as the all-powerful master of the universe, it has very little meaning and certainly is not specific enough to draw logical or reasonable conclusions.

Exception: Ambiguous phrases are extremely common in the English language and are a necessary part of informal logic and reasoning.  As long as these ambiguous phrases mean the same thing in all uses of phrases in the argument, this fallacy is not committed.


Jevons, W. S. (1872). Elementary lessons in logic: deductive and inductive : with copious questions and examples, and a vocabulary of logical terms. Macmillan.

Registered User Comments

Joe Walker
Saturday, January 21, 2017 - 01:31:28 PM
Have I committed any fallacies in the following, if so, how could I fix it?
A hole in ground in not anything
It is only the absence of dirt
Atheism is the absence of the belief in God
Therefore it follows that atheism is not anything

login to reply
2 replies
0 votes
Reply To Comment

Bo Bennett, PhD
Saturday, January 21, 2017 - 02:47:28 PM
There are many things wrong with that, but I will stop at the first self refutation. You call identify something as "hole", then you say it isn't anything.

login to reply
0 votes
Reply To Comment

Thursday, October 04, 2018 - 09:14:25 AM
As for this assertion tou might want to look up the following 2 fallacies on this site: weak analogy and the definist fallacy.

Furthermore both absence of dirt and absence of the belief in (any) God are something and are not related to each other.

login to reply
0 votes
Reply To Comment

Thursday, February 22, 2018 - 07:40:17 PM
Is this an example of equivocation?

It is a good idea to listen to victims of theft. Therefore if the victims say to have the thief shot, then you should do that.

The definition for "listen to" is equivocated here. In the first case it means listen to their personal account of the experience of being a victim of theft. Empathize with them. In the second case "listen to" means carry out a punishment of their choice.

login to reply
1 reply
0 votes
Reply To Comment

Bo Bennett, PhD
Thursday, February 22, 2018 - 09:22:58 PM
Yes. That is a good example.

login to reply
1 votes
Reply To Comment

Become a Logical Fallacy Master. Choose Your Poison.

Logically Fallacious is one of the most comprehensive collections of logical fallacies with all original examples and easy to understand descriptions; perfect for educators, debaters, or anyone who wants to improve his or her reasoning skills.

Get the book, Logically Fallacious by Bo Bennett, PhD by selecting one of the following options:

Not Much of a Reader? No Problem!

Enroll in the Mastering Logical Fallacies Online Course. Over 10 hours of video and interactive learning. Go beyond the book!

Enroll in the Fallacy-A-Day Passive Course. Sit back and learn fallacies the easy way—in just a few minutes per day, via e-mail delivery.

Have a podcast or know someone who does? Putting on a conference? Dr. Bennett is available for interviews and public speaking events. Contact him directly here.

About Archieboy Holdings, LLC. Privacy Policy Other Books Written by Bo
 Website Design and Software Copyright 2018, Archieboy Holdings, LLC.