Bob and Alice disagree regarding subject X.

Alice holds view A regarding subject X.

Bob holds view B regarding subject X.

View A and view B are quite contradictory views. Both can not be true at the same time.

Subject X is of paramount importance, but it is a very complex, technical issue. To fully understand subject X, therefore, you need to study for a long time in a university. Most people who really understand subject X, and have a truly informed opinion, hold doctorate degrees in something related to subject X. Since subject X is so important, many professors have to get together and discuss subject X. Sometimes those professors release public statements regarding subject X.

Those professors all have degrees in things like physics, chemistry, biology, mathematics, statistics and engineering.

Bob and Alice haven't studied any of those subjects. Therefore, they don't understand subject X really well. Bob and Alice both agree that neither of them has the proper expertise to hold an informed opinion regarding subject X. All they do is listen to the public statements given by the professors regarding subject X.

Out of the people who have the necessary expertise regarding subject X, 93% hold view A. (Group 1)

The remaining 7% of such people hold view B. (Group 2)

There are thousands of scientists in each group.

Subject X has tremendous political, cultural, historical, financial, religious and diplomatic implications. If view 1 was true, the world would look quite different from what it would like if view 2 was true.

Alice doesn't question Group 2's technical expertise, but she suspects they may (either subconsciously or knowingly)

  • Be politically motivated
  • Be affected by a conflict of interest
  • Be religiously motivated
  • Have personal/emotional biases
  • Be otherwise unable to think clearly regarding this particular issue, due to the immense implications of the matter

Bob says the same thing about group 1.

During a discussion regarding subject X, Alice says to Bob:

View A is true, because the majority of experts hold view A. Only a minority of experts believe B. It's a fringe view. Therefore, view A is scientifically correct, and view B is incorrect.

Is Alice's argument a form of the logical fallacy called "appeal to authority"? (The authority in this case being the experts in group 1.)

An argument from authority (Latin: argumentum ad verecundiam), also called an appeal to authority, is a logical fallacy that argues that a position is true or more likely to be true because an authority or authorities agree with it.

What about the "consensus fallacy"?

If many believe so, it is so.

Or does the consensus fallacy only apply when the "many" are the majority of a population at large, and not when they are the majority of experts in a certain field?

Is Alice committing any of these two logical fallacies?

And/or is she committing any other logical fallacies?

And to everything: Why? Or why not?

  • it depends on context and intention. it would be a fallacy if you were writing in a peer review journal and trying to prove it that way
    – user6917
    Jun 25, 2016 at 22:30
  • @MATHEMETICIAN And when would it not be?
    – Fiksdal
    Jun 25, 2016 at 22:33
  • if neither party has enough knowledge to prove it themselves
    – user6917
    Jun 25, 2016 at 22:38
  • 1
    @MATHEMETICIAN I see. Hopefully someone will be able to post a good answer.
    – Fiksdal
    Jun 25, 2016 at 22:42
  • 1
    Science itself doesn't "assert truth" regarding results. So anyone trying to "assert truth" about scientific results (including scientists themselves) is out of line. Even before you get to the "consensus" question. So I would say "category error" all around.
    – Jeff Y
    Jun 27, 2016 at 16:25

5 Answers 5


The main thing to realize about informal fallacies is that they are all closely related to strong arguments, because it's the resemblance to a strong argument that makes them seem compelling. In this case, the fact that an substantial majority of the people who seemingly have relevant expertise on the issue have come to a unified conclusion does not prove that conclusion to be true. But it does provide significant support for the conclusion.

If Bob has a definitive proof of his conclusion it outweighs Alice's collection of experts. But if Alice and Bob are both drawing conclusions based on similar types of arguments, then Alice's is stronger than Bob's. They aren't just comparing two opinions here --rather, they have agreed to take the consensus of relevant experts as supporting evidence for a conclusion, and that consensus is significantly stronger on one side than the other.

"Argument from authority" is an especially tricky fallacy because we're so often forced to rely on experts in the modern world. The key to avoiding it is a) make sure the authority is relevant b) in as much as possible, examine and evaluate the arguments and the evidence provided by the experts yourself and c) don't overreach on the conclusion.

  • 1
    I'd say "the authority is relevant (maybe 'competent') and trustworthy". A competent authority may be lying.
    – gnasher729
    Jun 27, 2016 at 18:27

Fallacy, shamallacy -- don't try to short circuit analysis by playing pin the fallacy on the argument. Whether Alice's statement is an appeal to authority depends in detail on what her intended meaning is, and how Bob interprets it.

If Alice intends (or Bob interprets) the statement as indicating that "we should defer to these people on this issue because of their [social|political|intellectual] standing" then it would be problematic. Note that Locke's original name for the fallacy is the "argumentum ad vericundiam" which I'll translate as "the argument to deference" -- i.e. an argument that in some moral/social sense you should defer to people of elevated status (c.f. this paper by J. Goodwin which includes an interpretation of Locke's formulation near the end).

If instead, both Alice and Bob interpret this statement to be a quick way of stating something like "These experts have looked at topic X in detail (which we don't have the resources to do), and are reporting on what they found; thus we should give credence to what they say", then the findings of the experts need to be assessed subject to the same considerations as other testimonial evidence. This is why both sides point the the bulleted items in the OP: these types of factors are the kinds of things that can bias peoples' testimony and thus degrade its reliability.

There is the same kind of breakdown in terms of the appeal to consensus: in one case you interpret the existence of consensus as "a thing" and thus should defer to it, which corresponds to the argument from consensus. The other interpretation is that the consensus is a summary of the conclusions of the group of experts involved. In which case it falls back to, collective, testimonial evidence.


In most cases, it is impossible or impractical to find the truth 100% reliably. Sometimes it is not impossible, but impractical for me because it would take huge effort. So instead of establishing the truth with 100% certainty, or trying to do so, we often only try to find the truth with a reasonable degree of certainty, so we can make informed decisions that are not 100% guaranteed to be correct, but at least have a reasonable chance of being correct.

Sometimes people reject any argument that doesn't 100% establish the truth as a "fallacy". That does to some degree miss the point. In the example, having 93% of all eminent scientists agree with a statement (and 7% disagree) isn't 100% evidence for the truth of the statement, but it makes it quite likely that I'm better off assuming it is true than assuming it is false.


From the background story, I think it seems that Alice is committing a fallacy of appeal to consensus (argumentum ad populum). She is saying that her view is correct because it is supported by majority. It would be appeal to authority if Alice had the belief that the group that affirms her views had more authority than the other group (that denies her views). But as you have pointed out (Alice doesn't question Group 2's technical expertise), it seems Alice gives same authority to both groups but is just using numbers. Interestingly Argument from Authority may involve a single person (expert/authority) only.

For e.g.

In 1923, leading American zoologist Theophilus Painter declared, based on poor data and conflicting observations he had made, that humans had 24 pairs of chromosomes. From the 1920s to the 1950s, this continued to be held based on Painter's authority, despite subsequent counts totaling the correct number of 23. Even textbooks with photos clearly showing 23 pairs incorrectly declared the number to be 24 based on the authority of the then-consensus of 24 pairs.

This seemingly established number created confirmation bias among researchers, and "most cytologists, expecting to detect Painter's number, virtually always did so". Painter's "influence was so great that many scientists preferred to believe his count over the actual evidence", to the point that "textbooks from the time carried photographs showing twenty-three pairs of chromosomes, and yet the caption would say there were twenty-four". Scientists who obtained the accurate number modified or discarded their data to agree with Painter's count.

(Source: https://en.wikipedia.org/wiki/Argument_from_authority)

Alice does not seem to be committing any other fallacy but she may be constructing an ad hominem in mind to explain away the views of Group 2.

I would however say as none of them (Alice and Bob) has any arguments for his/her side and both are incapable of constructing an argument in favour or against the proposition (Bob and Alice both agree that neither of them has the proper expertise to hold an informed opinion regarding subject X. All they do is listen to the public statements given by the professors regarding subject X.), it hardly matters as who is correct as none of the side is equipped to make the other believe or accept his/her view. It would be however a lot harder for Bob to justify his belief in view B, as compared to Alice who only has to cite majority in her favour.

Alice can avoid making fallacy if instead of saying view A is scientifically correct, and view B is incorrect, she says that view A is more convincing to scientific experts than view B. The thing that is important here is as Alice and Bob virtually know nothing about matter, they are only good for convincing each other as any other person with a little more knowledge, though maybe wrong, can effectively counter both of them. And if Bob does not believe that scientific consensus should be believed per se (Bob says the same thing about group 1.), even that will be a difficult task.

In short -

  1. Alice is committing a logical fallacy.
  2. Alice does have a stronger justification for her views than Bob seems to be having for his views.
  3. Unless Bob agrees or agreed to take into account view of majority scientists, he can, in my opinion, still hold his view and be as much justified in doing so as he was before.

Whether or not we call it a fallacious reasoning is beside the point. What is important is to work out what is at stake. I will try to explain (while acknowledging the above as a fallacy)...

Let's assume that your two persons don't understand the argument enough to construct a sound argument. That's quite likely, that even if both can construct some arguments, there's no way to tell which are more likely to be sound.

In this instance, the appeal to authority isn't valid, but it isn't a rhetorical fallacy

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A straw man is an example of a rhetorical fallacy. In effect, neither person has a "rational argument", but whoever is committing the fallacy of appealing to authority is more likely to be right. Just as they are not committing a rhetorical fallacy.

i.e. there's a difference between rational argument and a legitimately persuasive one.

  • hth and isn't too terrible :)
    – user6917
    Jun 25, 2016 at 23:11

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