A classic example is someone saying, "Gravity is only a theory." In this case they are committing a logical fallacy by conflating the everyday meaning of theory with the way the word is used in formal science.

I'm just looking for the official name of this fallacy.

  • can you give an example from philosophy?
    – user6917
    Commented Feb 20, 2017 at 20:16
  • @MATHEMETICIAN Not at the moment.
    – user4894
    Commented Feb 20, 2017 at 20:19
  • ok fair enough. i wonder how many there are, assuming you aren't talking about precision
    – user6917
    Commented Feb 20, 2017 at 20:21
  • 5
    It is 'equivocation' in the classical sense. en.wikipedia.org/wiki/Equivocation
    – user9166
    Commented Feb 20, 2017 at 20:28
  • 1
    wait, gravity is in fact only a theory. turns out newtonian gravity is wrong. may turn out that einsteinian gravity is wrong. no fallacy here.
    – user20153
    Commented Feb 20, 2017 at 22:11

3 Answers 3


The fallacy of ambiguity, or polysemy.

This fallacy includes the fallacies of equivocation, conflation, composition and such as well as your case of mixing technical terminology and ordinary usage. Conflation can also be considered a continuum or equivocation fallacy, but in particular conflation is the merging of two different things. Ambiguity, being open to more than one interpretation, more accurately describes the general fallacy.

Depending on the argument, the mis-use of technical jargon can also be an argument from false authority, or an example of a rhetorical device of "argumentum ad ignorantiam" which relies upon the audience's ignorance. Stating "gravity is just a theory" is not, however, an argument.

An argument that

  1. gravity is a theory, and,
  2. all theories are opinions, therefore
  3. gravity is an opinion

...is an example of an informal fallacy, i.e. a valid and unsound argument predicated upon a fallacy of ambiguity that misrepresents the truth.

  • 1
    I wonder how many fallacies of ambiguity involve such "homonym" problems at their root!
    – Joseph Weissman
    Commented Feb 20, 2017 at 19:48
  • @JosephWeissman indeed (& in deed...) Syntactical amibguity as well, e.g. "I like her cooking", "flying planes can be dangerous", "the shooting of the hunters is terrible" etc.
    – MmmHmm
    Commented Feb 20, 2017 at 19:53
  • Hmmm ... conflation is "comparing apples to oranges" in the link you gave. In this case we're comparing theories to theories, but with different meanings applied to the two terms. Ambiguity maybe. Even that's a little bit off target but relatively close. I'm specifically looking for the ambiguity between an everyday usage of a word and it's technical usage in a specialized field.
    – user4894
    Commented Feb 20, 2017 at 19:53
  • @Mr.Kennedy Your ambiguity link (which wan't Conservapedia) gave the example of a sign that said "Fine for parking," which a driver interpreted as being, well, fine for parking. I thought that was pretty funny but not exactly what I'm looking for. If they confused fine for parking with the fine structure constant in physics, that would be what I'm looking for. Ambiguity between everyday and technical meaning. I've been Googling and can't find anything yet.
    – user4894
    Commented Feb 20, 2017 at 20:17
  • 1
    I think ambiguity is as good as it gets. Evidently no special term for when one of the meanings is a term of art in a specific technical context. The polysemy reference is interesting.
    – user4894
    Commented Feb 22, 2017 at 5:47

Where there is no logic, there can be no logical fallacy.

"Gravity is only a theory" is simply a statement. It might be understood by a listener in a different way than intended by the speaker, but it is not logically fallacious.

For example:

1. To be blue is to be sad.
2. The sky is blue.
Therefore, the sky is sad.

This is logically fallacious since "blue" is being used to draw a conclusion about the sky, but the two premises use two different meanings of the word ("blue" as in sad; "blue" as in color).

If someone simply said "the sky is blue", this would not be a logical fallacy. One listener might hear it as "the sky is [the color] blue" and another listener might hear it as "the sky is sad", but there would be no logical fallacy on the part of the speaker.

  • The fallacy is going from "gravity is described by experts as a theory" to "gravity has the attributes commonly associated with things described as theories". Commented Feb 20, 2017 at 23:11
  • This is equivocation.
    – bdsl
    Commented Feb 20, 2017 at 23:56

The fallacy is the fallacy of four terms. A categorical syllogism may have three and only three terms: subject, predicate, and middle. Using one of the terms in two different senses unravels what might otherwise be a valid syllogism. At best, the reasoner ends up with the ambiguity described by Mr. Kennedy; at worst, there is no coherent statement at all.

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