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Welcome! This is the place to ask the community of experts and other fallacyophites (I made up that word) if someone has a committed a fallacy or not. This is a great way to settle a dispute! This is also the home of the "Mastering Logical Fallacies" student support.


Dr. Bo's Criteria for Logical Fallacies:

  1. It must be an error in reasoning not a factual error.
  2. It must be commonly applied to an argument either in the form of the argument or in the interpretation of the argument.
  3. It must be deceptive in that it often fools the average adult.

Therefore, we will define a logical fallacy as a concept within argumentation that commonly leads to an error in reasoning due to the deceptive nature of its presentation. Logical fallacies can comprise fallacious arguments that contain one or more non-factual errors in their form or deceptive arguments that often lead to fallacious reasoning in their evaluation.

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Krista Neckles

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Krista Neckles


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Mon, Mar 25, 2019 - 01:26 PM

Hello. What fallacies are committed in these passages?

What fallacies do you detect in these passages:
"Dozens of plants and animals are being wiped out every year, even though we have laws to prevent it. Clearly, we should repeal the Endangered Species Act", and
" People are driving their cars like maniacs tonight. There must be a full moon".
Thank You in advance! I found these passages from an introductory logic textbook I am reading.



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Phillip Goldstein

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Print Wed, Mar 27, 2019 - 01:08 AM
False Choice.

Non sequitor.


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Kaiden

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Kaiden


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About Kaiden

I enjoy fitness, listening to and playing music, laughter, spending time with my grandparents and discussing ideas with other people. Intellectually, I am especially interested in topics in philosophy and theology. I am a student of philosophy at Indiana University.
Print Mon, Mar 25, 2019 - 05:26 PM
Hi, Krista!

It is appropriate to recognize both examples as enthymemes. They are invalid arguments but purport to be persuasive on the assumption that the audience agrees to certain unstated premises. These unstated premises assumed to be input by the audience are called “tacit statements”.

I think that the tacit statement that should be added to complete the first argument is: if dozens of plants and animals are being wiped out every year, even though we have laws to prevent it, then we should repeal the Endangered Species Act. Including this tacit statement, the completed argument would read:

1. Dozens of plants and animals are being wiped out every year, even though we have laws to prevent it. [the original premise]
2. If dozens of plants and animals are being wiped out every year, even though we have laws to prevent it, then we should repeal the Endangered Species Act. [the added tacit statement]
Therefore,
1. We should repeal the Endangered Species Act. [the original conclusion]

For the second argument, I think that the tacit statement that should be added to complete it is: people drive their cars like maniacs only if there is a full moon. Including the tacit statement, the argument would read:

1. People are driving their cars like maniacs, tonight. [the original premise]
2. People drive their cars like maniacs only if there is a full moon. [the added tacit statement]
Therefore,
3. There must be a full moon. [the original conclusion]

I think that the tacit statements I add are faithful to how the defenders of these arguments would intend to argue. In this case, each of the completed arguments is valid. They also contain no fallacies, as far as I know, though there are hundreds of fallacies and I don’t know them all. However, in each case, you should doubt the truthfulness of the second premises (the tacit statements). The arguments are not good argument, but not because they are invalid or fallacious. Rather, they are not good because they contain at least one false premise.

In sum, each argument is invalid as given in your post. However, they should be recognized as enthymemes. I attempted to add the appropriate tacit statement(s) and have found that the completed arguments are valid and, to answer your questions, not fallacious. However, the arguments are not good arguments.

Thank you for your question, Krista

From, Kaiden


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Jacob

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Print Sun, Apr 07, 2019 - 12:47 PM
The first one is an example of the Nirvana Fallacy. It does not follow that because some plants and animals go extinct that laws to protect them are useless. If there were no laws then plants and animals would die at a faster rate. The gun lobby makes this argument: Why make laws to prevent law abiding citizens from buying guns when criminals get them illegally? Well all gun control laws work to prevent some people from getting guns. It is really hard to stop them all but every bit of regulation helps.


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Colin P
Tuesday, March 26, 2019 - 05:13:41 PM
@Kaiden: I like your answer but if you unpack the first example further is it not clearer? And are the potential places for disagreeing with the argument not clearer too? Viz:

1. Dozens of plants and animals are being wiped out every year
2. The Endangered Species Act was enacted to prevent species being wiped out
Therefore:
3. The Endangered Species Act is ineffective
4. We should repeal ineffective Acts
Therefore:
5. We should repeal the Endangered Species Act

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Kaiden
Tuesday, March 26, 2019 - 06:35:38 PM
Hi, Colin P!


What you have is a model example of adding tacit statements to an argument. When adding tacit statements to an enthymeme, it is important to try to add only statements that are faithful to the intentions of the arguer and that make the completed argument as strong as possible without making it seem like an unreasonable argument to make. And you don’t want to clutter the completed argument with more than what is necessary to fill in the missing premise(s). You’ve strived to meet all of those points, on behalf of the arguer.

Now, the arguer probably prefers to have a valid argument for his position. If you adjust your formulation so that premise two states “if dozens of plants and animals are being wiped out every year, then the Endangered Species Act is ineffective” (call this premise ‘2b’), then you can make the valid Modus Ponens inference to the intermediate conclusion 3 from premises 1 and 2b, making the entire argument from 1-5 valid. Instead of directly supporting the intermediate conclusion 3, your statement in premise two would be better offered by the arguer as a direct support for premise 2b.

I like it, Colin.

From, Kaiden

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Colin P
Wednesday, March 27, 2019 - 12:41:56 AM
@Kaiden:
Hi Kaiden, why do you think it's necessary to repeat premise 1, "Dozens of plants and animals are being wiped out every year," as a condition within your reformulated premise 2b, as in, "if dozens of plants and animals are being wiped out every year, then..."? Doesn't a premise draw out a condition into a separate entity that need not be repeated as a condition in another entity later? Colin

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Kaiden
Wednesday, March 27, 2019 - 07:45:56 PM
@Colin P:

Hi, Colin!


That’s a good question. I assume that the arguer prefers a valid argument. One possible tacit statement to add to the argument so as to make it valid, is a tacit statement that allows for a Modus Ponens inference to be made from the premises to the conclusion. Modus Ponens requires an argument to have a premise containing a conditional statement and a premise containing a statement that affirms the antecedent of that conditional statement. For instance:

1. The dog is happy.
2. If the dog is happy, it will wag its tail.
Therefore,
3. The dog will wag its tail.

Only by having a conditional statement and a statement that affirms the antecedent of that conditional statement, is a Modus Ponens inference possible. In my formulation of the Endangered Species Act, I wanted to be able to construct it in a way that allows a person to make a Modus Ponens inference. So, I needed a premise containing a conditional statement and a premise containing a statement that affirms the antecedent of that conditional statement. In light of this, the same statement would have to appear in two places—as a simple statement that is being affirmed and as the antecedent of a conditional statement. The original argument already had an affirmed statement, so the tacit statement that I need to add in order to complete the argument so as to allow for Modus Ponens, is a conditional statement in which the antecedent is the proposition that Premise 1 is affirming.

To be clear, this does not mean that premise 1 has been repeated. Premise 1 asserts that dozens of plants and animals are being wiped out every year, even though we have laws to prevent it. This assertion is made nowhere else in the argument. The statement IN premise 1 appears again, now in premise 2b. This time, we do not have an assertion that the statement is true (which is what premise 1 is). Instead, what is being asserted in the new premise is that the truthfulness of the statement in premise 1 is sufficient for the truthfulness of this other statement.

Anyone would be right to recognize that adding a tacit statement that allows for a Modus Ponens inference to be made is not the only way to make the completed argument valid.

Example One: Disjunctive Syllogism inference
1.) Dozens of plants and animals are being wiped out every year.
2.) Dozens of plants and animals are not being wiped out every year or the Endangered Species Act is ineffective. [added tacit statement]
Therefore:
3. The Endangered Species Act is ineffective.

Example Two: Modus Tollens inference
1.) Dozens of plants and animals are being wiped out every year.
2.) If the Endangered Species Act is effective, then it would not be the case that dozens of plants and animals are being wiped out every year. [added tacit statement]
Therefore,
3. The Endangered Species Act is ineffective.

All of these examples include tacit statements that would make the argument valid without including a Modus Ponens inference. (Then, of course, you would go on to add the premises necessary for tie in #3 to the arguer’s original conclusion). But for each of the inferences in these examples to work, the same statement must appear twice because these inferences work by affirming or denying one part of a compound statement, just like what Modus Ponens does.

Am I explaining this well? I’m glad you are interested in inferences and how sentences are evaluated in logic. There is an old book, “forall x: Calgary Version” that I read and it has been one of many helpful sources for me to refer back to. Any two given logic professors likely have slightly different styles, definitions and syntax for when they work in logic. For instance, some refer to the Modus Ponens inference instead as “implication elimination”; some logicians say “proposition” instead of “statement”; some logicians conjunct propositions in symbolic logic with “•”, and others do so with and upside down “V” shape. That is to say, different authors teach logic in different ways, but it’s all the same enterprise. The book I named is good introductory material to these basic concepts and you can use it to teach yourself formal logic. I think you should follow your interest and give it a go!

From, Kaiden

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Kaiden
Wednesday, March 27, 2019 - 07:59:36 PM
@Colin P:

The book can be downloaded as a pdf.

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Colin P
Saturday, April 06, 2019 - 12:05:43 PM
@Kaiden: That's helpful Kaiden. In your original post you write, "...the arguments... are not good because they contain at least one false premise." I would appreciate it if you would clarify, i.e. make explicit, what is false in the premise you added into the first example, the one we are discussing?

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Kaiden
Wednesday, April 10, 2019 - 03:56:06 PM
@Colin P:
Hi, Colin!

I state in the second-to-last paragraph of my Answer to Krista that the truthfulness of the second premise of my reformulation should be doubted. Check two sentences prior to the sentence you quote. What do you think, is the tacit statement I add probably false?

From, Kaiden

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Kaiden
Wednesday, April 10, 2019 - 06:36:35 PM
@Colin P:
I see, are you wondering WHY I think the second premise is false?

Well, the second premise is a conditional statement. So, if the antecedent is true and the consequent is false, then the entire conditional is false. I suspect that a zoologist, or whoever may have the relevant education, could make a compelling case that dozens of creatures are being destroyed every year, but the Endangered Species Act should remain in place. Because I suspect that a zoologist, or a relevant expert, could successfully make such a case, I think the second premise is false.

Unlike Jacob, it’s not obvious to me that a “compelling case” against the original argument would say anything about the argument committing the Nirvana Fallacy. It was in your reformulation, Colin, that the idea of the ineffectiveness of the Act was suggested. The original argument does not give the ineffectiveness of the Act as a reason for accepting the conclusion. Again, the original argument appears to be an enthymeme, leaving out certain statements that the audience is assumed to already agree with. Your reformulation seems reasonable to me, but a different audience might have added tacit statements that make the original argument valid, that are faithful to what the original arguer may have wanted, AND that avoid the Nirvana fallacy.

I hope I understood your question correctly this time, Colin. Thank you for requesting that I elaborate on my answer.

From, Kaiden

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Colin P
Thursday, April 11, 2019 - 02:44:15 PM
@Kaiden:

I prefer to know your reasons, now given, otherwise I am likely merely to impute to you my reasons. Moving on, I think it would be normal to state the conditional first, then the antecedent and then the consequent. Viz. 1) If A then B, 2) A, therefore 3) B. Subjectively this puts a focus on the conditional, and in many formal studies the conditional can be where the proving effort is greatest.

Colin

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Kaiden
Tuesday, April 23, 2019 - 12:04:46 PM
@Colin P:
Hi, Colin!

When Modus Ponens is defined, the conditional statement is virtually always the first of the two premises given. In this sense, your observation is very true.

Out in the world, however, I typically analyze and evaluate arguments in the structure in which they are presented by the arguer. In regards to the Endangered Species Argument, for instance, you should remember that the conditional statement that I added was a tacit statement. In other words, because the arguer believes that he and the audience share an implicit agreement with the tacit statement, he would probably not have an interest in including it where the focus or proving effort is greatest, even if the tacit statement were a conditional statement. Moreover, it feels numerically natural to assign “2” to a statement that has been added. These two reasons are why I take comfort in my organization of the reformulation of the argument.

Interestingly, even when a Modus Ponens form of argument is organized with the same structure as the definition, it may still not have the greatest proving effort on the first premise or even wherever the conditional statement is. Take the Kalam cosmological argument, for instance. It states:

1. Whatever begins to exist has a cause of its existence.
2. The universe began to exist.
Conclusion:
3. The universe has a cause of its existence.

In philosophical and scientific literature, the second premise seems to stir up more controversy than the first. This premise bursts with rich conversation about possible infinites, A or B theories of time, various cosmogonical models of the universe, and more. I think it receives much more attention between the two premises, although it is neither a conditional statement, nor in the first premise, nor both of those things.

With all of that said, I think it is very true that a classic Modus Ponens Argument form will have the structure that you have described, especially in formal studies. I only mean to say that outside of the textbooks, the nature of an argument becomes less tame.

Thank you, Colin. Also, if you took a look at that pdf book, I hope it is helping you learn more about logic! If you haven’t taken a look, that’s alright.

From, Kaiden

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Colin P
Tuesday, April 23, 2019 - 04:16:16 PM
@Kaiden:
Hello Kaiden, illuminating as always thank you. On your reminder I have just downloaded the book, I will make time to read it but as yet I don't know when.

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