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I got into an argument with a friend on MMA fighters and said that any fighter that gets caught PEDs should probably have an asterisk by his record. His defence was that could I say for sure that other fighters aren't using PEDs just because they haven't been caught. All that means is that they haven't been caught.

This kept going in circles and I kept saying that you can only go off what evidence you have but he kept repeating and then we just dropped it. I'm pretty sure his argument has to be logically flawed and was hoping for a better explanation of why.

Thank you

Sorry I didn't respond sooner. I thought some more about the conversation I had and I didn't structure my post properly. So when I said that the MMA fighter should have an asterisk next to his record, he argued that they shouldn't and those wins should count because you can't prove that others weren't cheating. What I'm having a hard time with is explaining that you can't make decisions about things you don't know. If the other fighters are using PEDs, and we have evidence then they should get punished too, but until then you shouldn't punish nobody because you can't prove others aren't using.

At this point I'm not particularly looking for a fallacy but I just want to know if his way is a valid approach. That you can't punish fighter X because fighter y is also cheating but just got lucky and wasn't caught.

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    Your "arguments" are not arguments, "should probably have an asterisk by his record" is just a judgment call. The asterisk presumably means that the person caught has been cheating throughout, which is a big leap from getting caught just once. Especially considering how spotty the testing used to be for not getting caught to mean much. Your friend is presumably making this point. But it is just another judgment call. Whose judgment is better is open to discussion, but either way it is not about mistakes in reasoning (fallacies). You can not derive what should be from what is by arguments.
    – Conifold
    May 14, 2019 at 0:39
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    Please be mindful of readers who not understand the references to "MMA fighters" who are "caught PEDs". May 14, 2019 at 5:22
  • You recommend a course of action. Quare? Jun 16 at 4:28

2 Answers 2

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Some general thoughts:

First:

The is/ought dichotomy suggests that there is no valid way to move from what is, to what ought to be.

You are saying: If we can prove X, then we should do Y. You're friend is saying: Let's not do Y because we can't prove R.

You've run into the is/ought dichotomy, so unless you can frame the context within an ethical system that you and your friend both agree on and will take its principles as axioms, then you're not going to get far.

What you can do, though, is try to break the discussion down into general principles:

Premise 1 (P1): Cheating is unfair.
P2: Cheaters should be punished.
P3: For all MMA fighters, if they are caught cheating, then we should do Y to them.
P4: Using PEDs is cheating.

P1 and P2 should be easy to get consent on. P3 is going to be a hard sell. You don't have a way to logically PROVE that Y is the appropriate punishment, and hopefully this forces you to recognize your own assumptions/biases (not that you should abandon them, but you should be aware of them).

Secondly:

I suspect you were remembering the fallacy called an appeal to ignorance where someone says: Because you cannot prove ~X, then X is true. The classical example would be: There is proof that ghosts are not real, therefore ghosts are real.

You're friend is saying: You cannot prove Fighter 2 isn't using Drugs.
That LOOKS like: You can't prove ~D,

but your friend is NOT saying: You can't prove Fighter 2 isn't using drugs, therefore he is using drugs. So your friend is not committing this fallacy, strictly speaking.

Thirdly:

Logic only applies to statements (sentences) expressed in the indicative mood. It sounds, based on your post, that you and your friend were speaking in the subjunctive mood. It doesn't mean that you couldn't translate your discussion into an argument, but the fact you are using the wrong mood is an indicator that logic may not the right tool for the job.

References:
Is-ought dichotomy
Subjunctive Mood

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  • Sorry I didn't respond sooner. I thought some more about the conversation I had and I didn't structure my post properly. So when I said that the MMA fighter should have an asterisk next to his record, he argued that they shouldn't and those wins should count because you can't prove that others weren't cheating. What I'm having a hard time with is explaining that you can't make decisions about things you don't know. If the other fighters are using PEDs, and we have evidence then they should get punished too, but until then you shouldn't punish nobody because you can't prove others aren't using. May 15, 2019 at 6:45
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It is not a formal fallacy because it was not in a formal argument.

In terms of logic and philosophy, a fallacy is a flawed argument format. It is often viewed as a pattern of reason that is invalid in its structure. It is possible to have a logical fallacy and still arrive at a correct solution.

It is in fact possible to a have a persuasive and defeasible argument that involves something that would be a logical fallacy if it were claimed to be part of a formal argument and claimed to lead to a logical proof.

Logical fallacies can include ad hominem attacks, appeals to authority, and slippery slope arguments. But note that all of those are fallacies only if incorporated into something that purports to be a logical argument leading to a formal proof or something akin to a formal proof. Each of these can be reasonable and defeasible when discussing policy and all of them are used routinely in courtrooms.

Your friend's argument, at least as you describe it, was not structured as a formal logical argument. Instead, he was making a normative argument about how he believed things should be and providing defeasible reasoning for this normative argument. In that case, it was not a logical fallacy.

If he had claimed to be making a logical argument, then it could arguably be a non-sequitur.

Non sequitur literally translates as "it does not follow". In formal logical, it means that the conclusions does not follow from the premises. Notably, while it is always a fallacy, it can sometimes be a fixable fallacy. Sometimes one merely needs to introduce additional steps to show how one thing does lead to another.

The early unpublished version of Andrew Wiles' proof of Fermat's last theorem famously contained a gap, which meant that strictly speaking it contained a non sequitur. That was corrected by adding a necessary lemma with the help of a collaborator (Richard Taylor).

As Rob points out, the is-ought dichotomy means that any attempt to formally get from a factual position to a normative one requires either taking some sort of "ought" statement or moral position as an axiom or will inevitably have some sort of structural flaw, often some form of non sequitur. However, outside of formal logic, we use reasoning that involves both sides of the dichotomy all the time, particularly in law and policy.

As long as he was taking a normative position, rather than claiming to take a position in formal logic, your friend did not commit a fallacy. In fact, based on the synopsis you provided, I suspect his argument is more persuasive than yours. To deliberately invoke a slippery slope argument, taking your reasoning to its conclusion could involve letting criminals off because we know we aren't catching all of them.

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