Fallacy of ambiguity

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Cogito ergo sum
Logic and rhetoric
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General logic
Bad logic
Claim X is made. Y is concluded based on an ambiguous understanding of X.
Logically Fallacious[1]

A fallacy of ambiguity occurs when a conclusion is drawn from premises that are unclear. When an unclear premise is used, it may not support the conclusion.

Alternate names[edit]

Several names exist, including:[1]

  • Vagueness
  • Amphiboly
  • Semantical ambiguity
  • Type-token ambiguity


In essence, the fallacy involves two steps:[2]

  1. Premises are presented that are unclear enough to allow for more than one conclusion.
  2. A single conclusion is drawn from these premises.


Here are two examples:[1]

P1: It is said that we have a good understanding of our universe.
C1: Therefore, we know exactly how it began and exactly when.

P1: All living beings come from other living beings.
C1: Therefore, the first forms of life must have come from a living being.
C2: That living being is God.

In US law[edit]

In United States law, the vagueness doctrine holds that Constitutional law (those laws applied between the government and individuals) must clearly define what is punishable. Criminal laws that do not clearly define what is punishable violate the due process clause of the Fifth Amendment and Fourteenth Amendment of the United States Constitution.[3] Statutory laws can also be ruled as void for vagueness due to their leading to arbitrary prosecutions.[3] The vagueness doctrine does not apply to private law, i.e., law between private parties such as contract law.


  • Fallacy of accent, where the stress of a word or words is unclear and makes the meaning unclear
  • Fallacy of amphiboly, where grammatical uncertainty makes the meaning of a sentence unclear
  • Equivocation, where one word has two or more separate meanings that are switched between in the course of a sentence
  • Quote mining, where context is removed to make a point (which the context may disprove, downplay, or explain)
  • Phantom distinction, where two functionally synonymous terms are treated as separate
  • Moral equivalence, where two distinct moral/immoral ideas are treated as equally moral/immoral
  • Wronger than wrong, where two partially false ideas are treated as equally false

See also[edit]

External links[edit]


  1. 1.0 1.1 1.2 Ambiguity Fallacy Logically Fallacious.
  2. 30 More Fallacies A Philosopher's Blog.
  3. 3.0 3.1 Vagueness doctrine Legal Information Institute, Cornell Law School.