Fallacies of Presumption, Ambiguity, and Grammatical Analogy


Begging the Question

God exists because it says so in the bible. Furthermore, we know that the bible is true because it is the revealed work of God.

Occurs when the argument assumes some key piece of information

Sometimes the key information is left out of the argument

Sometimes the conclusion is restated in slightly different language in the premises

Sometimes the reasoning is circular where a key premise depends on the conclusion.

Complex Question

I understand that your tax return is being audited again. Are you still cheating on your taxes?

Occurs when a single question is really two (or more) questions that are asked; a single answer is applied to both questions.

Not to be confused with leading questions, in which the answer is somehow suggested in the question

False Dichotomy

Either you contribute to the American Cancer Society, or you don't care about finding a cure for cancer. The choice should be clear.

Occurs when a disjunctive premises incorrectly presumes that the two alternatives are exhaustive.

Suppressed Evidence

During the past 10 thousand years, no human has ever set foot on Mars. therefore, it is unlikely that nay human being ever will set foot on Mars during the next 10 thousand years.

Occurs when an argument ignores key evidence that would lead to a very different conclusion.


Peter is a terrible violinist. But a violinist is a human being. So, Peter is a terrible human being.

Occurs when the conclusion depends on the fact that a word has been used in two different senses. Sometimes the shift in meaning is subtle.


Cyndi said that she saw a man walking a dog through her window. Clearly that man should be charged with animal abuse.

Occurs when a syntactical ambiguity results in a faulty interpretation that is used to support a conclusion. The ambiguity usually arises from a mistake in grammar or punctuation.

Not to be confused with equivocation, which has to do with meanings not syntax.


Each atom in this table is invisible to the naked eye. Therefore, this table is invisible to the naked eye.

Occurs when the conclusion depends on the erroneous transfer of an attribute from the parts of something to the whole.

Sometimes the transfer of attributes is legitimate.

Not to be confused with hasty generalization. Composition proceeds from members of a class to the class itself. Hasty generalization proceeds from specific to general (from some members of a class to every member of a class).


This thousand dollar bill is very valuable. Therefore, if it is torn up into a hundred pieces, each piece should be valuable.

Occurs when the conclusion depends on the erroneous transfer of an attribute from the whole to the parts of something.