Is it fallacious to argue "you can't say X because you lack authority"?

Question

So I understand an Argument from Authority, or ad verecundiam, fallacy is where someone uses a persons/their authority to reason their argument without other sound evidence. But what in a situation like this:

Person A: What is the maximum sentence someone can get for assault?

Person B: According to this state's revised code, assault is a Misdemeanor I with a maximum jail sentence of 180 days and max fine of $2500.

Person C: You're not a lawyer or cop Person B, you don't know what you're talking about!

Why is Person C's argument fallacious? Is a lack of an authoritative position reason to void an argument?

Answer 1

I don't know what I would call this fallacy but I would say we can generalize the problem as confusing credentials with knowledge.

In other words, it doesn't matter what letters come before or after someone's name as to whether or not they might know (or not something).

At first, I want to say this is an informal fallacy, but I think we can actually describe it as a formal fallacy.

First off, I think we can reorganize the argument as follows:

1. If you were a lawyer, you would (could) know what you are talking about.
2. You are not a lawyer.
3. Ergo, you do not know what you are talking about.

This is a formally fallacious argument that is an example of "denying the antecedent." The fallacy is that there are of a number of ways that an individual could know what they are talking about which is not restricted to "lawyer" (substitute as necessary). In this case, the conditional identifies a sufficient condition.

In terms of informal fallacies happening in the argument, I suppose we could name this either an ad hominem insofar as it does not deny the claim of C but only attacks C's ability to make the claim or still an "argument from authority" or possibly an inverted argument for authority (to mark that the assertion is that an authority is necessary and absent).

Similar arguments need not necessarily be fallacious. For instance,

1. * If you speak Japanese, you understand what he is saying.
2. You don't speak Japanese.
3. Ergo, you don't understand what he is saying.

But here the language is deceptive, because in general we would take the first claim here not to be a simple conditional but rather a claim that is a necessary condition for understanding what he says.

I've marked the first sentence with a * because as far as formalizations go, this is an incorrect use of a conditional in normal logic, but it seems completely natural as English.

I mention this second example in part to state that similarity in the structure of the English alone is not enough to prove that the argument is fallacious.