"....I would probably just call an argument in the form "X is a horrible reason for doing Y, therefore Y is wrong" a non-sequitur. You could say it's a fallacious appeal to emotion potentially as well....."

Ok, this seems like an attempt to identify what's going on and categorize it. However, I am just going to guess there might well be an even better fallacy categorization.

"However, even though that particular statement is fallacious if offered as a proof it's not really very difficult to change it to be making a valid point. If the reasons being offered for doing Y are all horrible ...."

Ah, well, the word "all" here is a different matter.

"A false premise sets a false conclusion."

Hi - is this necessarily true? I am not asking this as a rhetorical question. I can see a couple of possible answers:

1. If the logical chain between premise and conclusion is strong, but the premise is false, then either the conclusion is wrong, or the conclusion is of indeterminate correctness. I'm not sure which.

2. if the premise is false and the logical chain to the conclusion is questionable, then the conclusion is not necessarily false, I'm thinking then it is not clear whether it is false or not.

@kmaz It's not necessarily true. That would be the fallacy of denying the antecedent (https://en.wikipedia.org/wiki/Denying_the_antecedent )

A false premise just means the argument is not sound, which doesn't say anything about the truth of the conclusion.

See also the difference between validity and soundness: [iep.utm.edu]

In Logic 101, a False Premise always sets a False conclusion. The "Conclusion" may be true if there are other true premises that preface it. But it is illogical to mark it so if one of them is false.

@lovemuffin

Thanks for this, it answers the question here, and possibly my original question for the thread. It appears that folks who respond to the really horrible premises and reasoning offered in some of the latest political discussions, and who then try to go on and imply or say that the opposite conclusions must be true, may be engaging in some form of the fallacy of the inverse.

Hi @Santanaman9

You wrote:
"In Logic 101, a False Premise always sets a False conclusion. The "Conclusion" may be true if there are other true premises that preface it. But it is illogical to mark it so if one of them is false."

Hi -

1. I am not sure we are remembering Logic 101 the same. Do you have a link for this claim that "A False Premise always sets a False conclusion"?

2. Also, there may be some confusion here as to terminology as to the use of the word "Sets" or the use of the word "False". I am not sure I have run across the word "sets" being used in this way. More importantly, are you using wording around "false" "conclusion" here to try to discuss whether an argument is invalid or unsound?

It's been too many decades for me to remember with confidence, but I'm guessing that a false premise and an invalid argument leads to an indeterminate conclusion, not necessarily to a conclusion which is shown to be false. If the false premise is loaded into an otherwise valid argument, even there, I'm not sure it necessarily means the conclusions are always false.

What I am asking about in my original argument is whether there is a term for (what I think is) the fallacy of assuming if a premise is false then the conclusions must necessarily always be false.

@lovemuffin

An ammendment to my previous comment - on consideration, while I like your response in order to address @Santanaman9's points, I think the original question I had is not yet answered (i.e.: the "fallacy of the inverse" may not quite be what I was looking for). To try to summarize:

If I look at some argument that someone has put forth and point straight at some fallacy I claim they have engaged in, and then I state that the opposite of their conclusion is proven true because either their premise is wrong or their reasoning is invalid, then presumably I have engaged in ("employed"?) a fallacy myself (and a whopper of one at that), but I'm hard-pressed to determine if there is a name for that fallacy.

Taking another quick look around, maybe it is the "argument from fallacy" or "argumentum ad logicam" ?

"...Description: Concluding that the truth value of an argument is false based on the fact that the argument contains a fallacy...."

[logicallyfallacious.com]

@lovemuffin

PS: Thanks for the link regarding validity and soundness. Good stuff.

@kmaz Right, the OP is not describing the fallacy of the inverse, that comment was about the idea that "a false premise means a false conclusion, (e.g. p implies q, not p, therefore not q). Although I guess you could say the OP describes something similar in spirit (your argument is bad therefore the conclusion is false), but the OP is focused on the "horribleness" of the argument which I took to mean something moral rather than just its logical validity.

I'm sure someone has thought of a pithy name for what the OP describes, but I don't know what it is and my quick skim of some sources on informal fallacies didn't turn up the exact thing you were looking for. But, I don't think it has to have a fancy name to be fallacious. You shouldn't expect every form of logical error to have a name. If I were arguing with someone employing this style of reasoning I would just try to explain it by using an example of the same kind of argument but one where the fallaciousness should be obvious. Maybe something like

P1) If an argument depends on a horrible premise then the conclusion is false

P2) "Murdering children is wrong because children should be kept alive in order to be tortured" is an argument with a horrible premise (that children should be tortured)

C) Therefore, murdering children is not wrong

The main point being to make clear the difference between an argument being unsound or invalid and its conclusion having some particular truth-value.

@lovemuffin

I'll respond more later, but please note in case it is not clear that I am the original poster.

@kmaz I know. By OP I meant original post and not so much original poster.

@lovemuffin

I think we are to an extent searching for what is already found (as far as I am concerned) so I will just spell it out where I am with this:

1. I did not mean to distract the conversation in my original post by using the word "horrible" in a somewhat confusing way. I was writing too quickly so that I could get to work on time and meant simply when someone offers a reason that seems (to us) clearly not-the-case.

2. I will say that indeed, the fallacy of the inverse does provide some of the answer, though perhaps not all of it. I also think that the argumentum ad logicam ("argument from fallacy" ) seems to apply, and (depending on the situation) probably some others.

The matter is somewhat complicated because it is kind of a "secondary fallacy". That is, the fallacy is on the part of a person first presuming to diagnose a fallacy and then incorrectly over-reaching to try to say that since a fallacy has been used, the inverse of the conclusion is implied or (if they really want to over-reach) can be assumed true.

3. Unless I am mis-understanding, @Santanaman9 has actually more than once provided us with an example of attempting to say that the fallacy of the inverse is not a fallacy at all but a basic or correct principle of logic. i.e.: he seems to be saying that a false premise necessarily leads to a "false conclusion". It is not clear whether by "false conclusion" he means this how it might be taken by some (that the opposite of the conclusion is true) or that the conclusion is simply un-supported and thus not clear. Still waiting for some sort of link from him.

4. I think being able to assign some categorization of fallacy in this case (and thus bring some improved understanding to what is going on, particularly if there is an extended pattern across many conversations) is of some more importance than you and others seem to be saying. @Santanaman9's apparent mis-understanding (in my view) helps me underscore my point here, as to importance, but the broader driver for me is that I think it is worth seeing if there is a pattern of use of this fallacy amongst the modern political "Resistance" in the US. I am not sure if I am actually correct in saying I see this that frequently, but the case would be that I sometimes see:

a) Some argument is offered which seems ridiculous to the listener, and indeed they may very well respond with a correct diagnosis of a false premise and-or bad reasoning following from premises.

b) However, the listener may then take a short-cut and undermine their own case by over-reaching and trying to say that, given the apparent ridiculousness of premises or apparently really sloppy and incorrect reasoning offered by the proponent of an argument, we should just kind of take a short-cut and move on and assume that the conclusion sought by the proponent can be assumed either besmirched, implied wrong or just flat out proven incorrect.

I do think there are other fallacies or principles which seem to come naturally in looking at this pattern, but the principles of the fallacy of the inverse and the argument from fallacy seem (to me) to be two decent toe-holds for trying to diagnose a pattern and (applying this to one set of cases) offer one attempted constructive criticism to members of the modern Resistance movement.

@kmaz Aha! it does look like Argumentum Ad Logicam is what you were looking for. Nice! I couldn't find it. The "bad reasons" fallacy.

I think that santanaman was just being a bit loose in his phrasing rather than committing the fallacy though. It gets tricky to distinguish between saying "this argument is wrong" and "the conclusion is false", but I think he really meant the former, because he went on to say that "the conclusion may be true if there are other true premises" in a followup.

Sometimes it's tricky to be as precise as one needs to be when discussing logic

Hi @lovemuffin:

yes, I think Argumentum Ad Logicam (Argument From Fallacy). One of the things I wanted to say is that I think Denying The Antecedent (Fallacy of the Inverse) also applies. Puzzling this over, I ran across this on wikipedia, which seems helpful to our discussion:

[en.wikipedia.org]

"...Form
It has the general argument form:

"If P, then Q.
P is a fallacious argument.
Therefore, Q is false.[6]
Thus, it is a special case of denying the antecedent where the antecedent, rather than being a proposition that is false, is an entire argument that is fallacious. A fallacious argument, just as with a false antecedent, can still have a consequent that happens to be true. The fallacy is in concluding the consequent of a fallacious argument has to be false."

So, both Argumentum Ad Logicam and Denying The Antecedent seem to be "formal" fallacies, and with some sort of similarity or overlap or proximity.

I had thought maybe the difference between "formal" and "informal" fallacies might at this point in the discussion be merely of idle interest, but as I look into it, there does seem to be some focus on the issues raised, so maybe for further discussion.

As to exact points and what each of us means or doesn't mean, I wasn't able to tell what Santanaman meant in all respects.

Having caused much of the migration throughout the world, do we have any right to prevent those migrants seeking refuge within "our" country? Why is it it ours in the first place?

@rogerbenham Oh boy can we ever get into a debate on this.If we are truly concerned about the life support system that supports ALL life we need to look at ways to lower our footprint. Bringing more people into the country with the worst footprint is not helping to relieve any stresses but only exacerbates them. This hurts everything (not just humans). Immigrants and citizens alike end up suffering.
I disagree that we are the source of much migration in the world. Many, many other countries are major contributors in wrecking the carrying capacity of their own country. I once submitted an article in the Smithsonian about Ethiopia where a former citizen was using satellite technology to track upcoming harvest crashes and alerting the UN world food program to send food to those regions. It was then shown that the era of food security in the country was actually leading to a doubling of the population within 20 years! A comment I just heard was the compassion has to be tempered with tough love. I totally agree.