Chapter 3, Tutorial 4
Fallacies of Ambiguity

There are lots of real reasoning problems when it comes to unclear language. We look at just a few ways.


My brain is a part of the universe, so the cosmos is a universal mind

Huh? This thinking about the brain is a bit fast, to say the least. Even if my brain thinks, it doesn't follow that the universe itself is a thinking thing. But often "metaphysical" or "philosophical" speculation jumps to such a conclusion.

Similarly, we wouldn't say that because every basic part of the universe is subatomic, o the whole universe is subatomic.

1. Reasoning from properties of the parts of an object to the claim that the whole object has these same properties is obviously fallacious. This is the fallacy of composition.

2. Likewise, if one reasons that the parts have the same properties as the whole, one is confused. Just because my brain thinks, doesn't mean the each neuron thinks. The parts taken together may have the property in question, but they need not have this property individually.

So, it is also a fallacy to argue that the parts of an object have all the properties of the whole. This is the fallacy of division.

















It all depends on what the meaning of the word "is" is

Dose anyone still recall President Clinton? He made this phrase famous. And yes, "is" can have various meanings.

We can mean it in

(1) a present tense way, "to be now", as in "He is in the house".


(2) a tenseless way, as in "the number 7 is greater than 3" or "Aristotle is one of the greatest philosopher-logicians of all time".

Perhaps Clinton was trying to confuse us about his statement to the grand jury (something about "is there an affair between you and woman X ").  there is some intent to deceive here and so maybe fallacious argument. Or maybe some good linguistics? This is probably best left to other sources than a logic book; Let me just quote another website:

Steven Pinker, Listening Between the Lines:

In his grand jury testimony, Mr. Clinton expounded on the semantics of the present tense ("It depends on what the meaning of the word 'is' is") and of the words "alone," "cause" and, most notoriously, "sex."

Clinton's rebuttal to the Starr report:

Literally true statements cannot be the basis for a perjury prosecution, even if a witness intends to mislead the questioner. Likewise, answers to an inherently ambiguous question cannot constitute perjury.

A joke:

Have you ever touched Paula Jones or Monica Lewinsky?
It depends on your definition of "or".

(Thanks to:


We do have a fallacy of reasoning whenever a word or phrase is used in more than one way. Or when the grammar confuses.

3. Begin with one sort of ambiguity: