A Logic Refresher - Classic (Informal) Fallacies

This is mostly a republication of an essay I published on Daily Kos on Tuesday Dec 15, 2009 10:09 AM PST. The current link to the original is http://www.dailykos.com/story/2009/12/15/814540/-Logic-Refresher-8211-Cl.... I have removed a bit of Daily Kos specific material and fixed some bad grammar and such. I wanted it over here in my archives for reference. I'm going to try to auto-publish it at an innocuous time and will be able to tend it only sporadically.

I had planned on diving straight into the fallacies under consideration here, but came to realize that I should first revisit exactly what logic is. Logic is a heartless and soulless study of reasoning, and the part of concern here is the analysis of the validity or invalidity of argument forms. Truth and falsity are properties of statements, assertions, allegations and the like, but not of arguments and argument forms. Argument forms are either valid or invalid and they are valid if and only if it is impossible for an argument of that form to contain true premises and a false conclusion. Thus, "All k are l and x is a k therefore x is an l" will always have a true conclusion, regardless of what is substituted for k, l, and x, so long as the premises "all k are l" and "x is a k" are true. Lastly, an argument with a valid form and true premises is sound, otherwise it is unsound, or "horseshit".

Fallacies are unsound arguments, of invalid form, that seem to be quite common and frequently fairly deceptive. The so called informal or classical fallacies are often divided into two categories, fallacies of relevance and fallacies of ambiguity. I shall take them up in that order.

FALLACIES OF RELEVANCE

Argumentum Ad Baculum is an appeal to force or threat of force; "do, say or believe x or else you will be beaten, arrested, fired, HRd, banned, or consigned to hell to burn forever."

Argumentum Ad Hominem is an argument "to the person" or about the person and comes in at least 3 flavors. The first, often called abusive is of the form "you, he, she or they are dorks, and therefore wrong". Technically, the full syllogistic version would be "You are (something bad). All (something bad) are wrong about everything. Therefore you are wrong about everything." In real life, one or more terms is often left merely implied, resulting in things such as: "He is a heathen, hence he is wrong", leaving the middle term "All heathens are always wrong" implicit, and even simply "Jackass!" leaving both the middle term and the conclusion implicit. Thus, something like "Jackass!", while it might simply be a gratuitous insult, can also be a variation of the abusive form of argumentum ad hominem. Of course, the argument form can be applied to actions and behavior as well as to ideas: "He must be a thief because he's a banker", for example.

The converse of the above, a sort of positive Argumentum Ad Hominem, is the argument that something must be true because the person stating it is a good or wise person. "He is a nice guy, ergo he is correct". This can also be used to hold that actions are good, true, honorable or whatever, just as the abusive form can be used to argue that certain actions are bad or evil or whatever. "He is a good husband and parent, therefore he cannot be an embezzler", for example.

The circumstantial form of Argumentum Ad Hominem is an argument from special circumstances. "You must accept x because the bible says so and you are a priest", or "because the GOP says so and you are a diehard GOP supporter". In short you are a hypocrite if you do not do or accept something. Another variation is to assert that the adversary's proposition must be rejected because it was dictated by the adversary's special circumstances - a producer supporting protective tariffs or a trial lawyer opposing so called tort reform - the adversary is clearly prejudiced in favor of the proposition and his/her arguments must therefore be but rationalizations of his/her self-interest driven stance. Strangely enough, a perfect hypocrite, taking both sides of every issue, will obviously be right half of the time, so calling somebody hypocritical cannot possibly, in and of itself, speak to the soundness of whatever argument they are proposing at the moment.

Argumentum Ad Ignorantiam is an argument from ignorance, generally of the form that x hasn't yet been disproved (and hence must be true). This pops up more often than one would expect, even though it is clearly without merit. It hasn't been disproved that so and so is an alcoholic, hence it must be true. "How can you possibly know that God doesn't exist?" is a slippery form of this argument.

Argumentum Ad Misericordiam is an Appeal to Pity. It is not so much used in arguing for or against a given proposition, but is mostly used in arguing for or against a course of action, such as the argument that one shouldn't jail some teenage ax murderer because he is an orphan.

Argumentum Ad Populum is an appeal to the majority, arguing that something must be true because the majority holds it to be true. It is a form of jumping on the bandwagon.

Argumentum Ad Verecundiam is an appeal to authority, but more properly, a misplaced appeal to authority. An appeal to a renowned civil rights lawyer's stated opinion on a question concerning the first amendment is technically not sound, she could still be in error, but what is really bogus is something like the days when everybody cited Aristotle, who was an authority on everything and an expert on almost nothing. Once upon a time we held scientists in great esteem, and they used to consult Dr. Teller on damn near everything, including low income housing, though he wasn't particularly well informed or perspicacious on much of anything except physics and politics.

The fallacy of Accident consists in applying a general rule to a specific incident where the accidental facts of the case render the rule inapplicable. If you lower the price of an item, sales will generally increase. If you lower the price of a niche specialty item sales might not increase if sales were constrained by the lack of further interested buyers independent of price (please, do not try to discuss this with academic economists).

The fallacy of Converse Accident, aka hasty generalization, generalizes a general rule from exceptional cases - any consumption of alcohol causes drunkenness; all pills remedy seasickness, all power hitters use steroids, etc.

False Cause is a class of fallacies including both non causa pro causa and post hoc ergo propter hoc. The first is general, the mistake of a something which is not cause of x for the cause x. The second is the belief that something which preceded x must have caused x. The english "False Cause" is usually used for any and all arguments that incorrectly assert a causal connection. (I am not sure how widely this has been expanded to include those who allege a single or unitary cause for things with multiple causes.) Few things in reality are monocausal. Exercise - read up on "proximate cause".

Petitio Principii is better known as begging the question and consists of incorporating the conclusion in the premises resulting in what is known as a circular argument. "I know god exists because he wouldn't fool me." (Descartes)

The fallacy of Complex Question consists in demanding or giving a single unified answer to a compound question such as "Have you given up heroin?" or "When did you quit taking opium?".

In each case there is the initial question of did you ever use the drug under discussion and the second question of whether or not you have stopped doing so, and, in the second case, the third question of exactly when you quit, if in fact, you did quit, if, in fact, you ever took it in the first place.

Lastly, Ignoratio Elenchii, or irrelevant conclusion consists of presenting an argument that, whether sound or not, doesn't address the issue in question. An example would be that of arguing that roads are important for commerce in a discussion of a particular specific plan for financing a particular specific proposed highway. It doesn't matter whether or not roads are important for commerce, it matters whether or not the proposed financing plan is workable or not.

This brings us to the

FALLACIES OF AMBIGUITY

Equivocation consists of confusing or interchanging different meanings of the same word - "end" means both goal and termination, this could lead to the equivocation: "an armistice, cease fire or treaty is the end of an armed conflict, hence the goal of warfare is an armistice, cease fire or treaty". The old joke "some cookies have chocolate chips; these cookies have chocolate chips; these cookies sure are some cookies!" is likewise equivocation. This is very common with relative terms - large, small, good, bad, peaceful, quiet, etc.

Amphiboly results from arguing from premises which are grammatically ambiguous. The fallacy occurs when a term in the premise is used in the form or interpretation which would result in the argument being true, but the conclusion is based on the interpretation under which it is false. A Classic example is the Oracle of Delphi telling a king "If you go to war, a powerful kingdom will fall", which the oracle allegedly intended as warning that the supplicant would be defeated, and which he took to mean that he would succeed.

The fallacy of Accent consists in making a statement that can be taken more than one way depending upon what accent is given to the words used. For example "Woman, without her man is nothing" versus "Woman without her man, is nothing". "We should not say bad things about the dead." has different meanings depending upon whether the emphasis is on "bad" or "dead". Of late, people have applied the term to misleading headlines, such as the following type
"WAR IN ZAMBIA
not likely"
which I find to be a bit of a stretch, but whattheheck.

The fallacy of Composition has two flavors:

1. Reasoning fallaciously from the properties of the part to the properties of the whole. For instance, claiming that since each element of a dish is tasty in its own right the dish as a whole is or must be tasty.

2. Reasoning fallaciously from the properties of the members of a set or collection to the properties of the set or collection. An example would be to argue that individual grains of sand are light, hence a 50 pound bag of builders' sand is light. Here we have a type of equivocation on two uses of "to be", distributive (grains of sand are light, barn owls are widespread) versus collective (a bag of sand is heavy, barn owls are birds).

The fallacy of Division also comes in two kinds:

1.Arguing fallaciously that what is true of the whole must be true of each of the parts, such as "My truck is heavy, ergo all of its parts must be heavy".

2. Fallaciously arguing from the properties of a collection to the properties of the members, such as "The set of integers is infinite, hence each integer is infinite". Here again there is an equivocation between the collective and distributive uses of "to be", the collective is infinite, but the distributive elements aren't.

That takes care of what I believe to be the most widely agreed upon set of "classical" or "informal" fallacies. They are by no means all of the fallacies out there. You may have noticed the absence of the "non sequitur", which is, broadly, any argument where the conclusion does not follow from the premises. More specifically, it is commonly used where the premises and conclusion are completely unrelated. In a sense, the first, broader meaning, would apply to all fallacies and improper arguments and even the second, to some degree. Nonetheless, back when I learned this stuff, it was generally classified as a formal fallacy, or otherwise held that the formal fallacies were all special cases thereof.

It is important to remember that while a the use of a fallacy in an argument renders the argument unsound and hence unconvincing and non probative, it does not mean that the conclusion is wrong. For example, it I were to argue that "all of the Popes have been idiots and therefore the earth goes around the sun and not vice-versa", I would be committing a fallacy, my argument would be unsound, unconvincing and non-probative. Nonetheless, my conclusion would still be true. (actually, both revolve around the system's center of mass, but why quibble)

Enjoy.

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enhydra lutris's picture

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That, in its essence, is fascism--ownership of government by an individual, by a group, or by any other controlling private power. -- Franklin D. Roosevelt --

elenacarlena's picture

And I wonder, if you posted it at TOP, how many people would wonder what you're trying to say about them, and how many of the above arguments would find their way into the Comments!

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Please check out Pet Vet Help, consider joining us to help pets, and follow me @ElenaCarlena on Twitter! Thank you.

It seems at TOP in the last six or so years since el published, people have used this as a how to manual, not as a warning.

(BTW, all that Latin is just Greek to me)

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There is no such thing as TMI. It can always be held in reserve for extortion.

enhydra lutris's picture

still lurking I noted an exchange regarding then candidate Obama

A) How do we know he isn't just saying x but planning y
B) Impossible. I have met the man and he is a person of character, so he would never do that.

[Offstage eyeroll by moi] I thought these folks were supposed to have their shit together ...

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That, in its essence, is fascism--ownership of government by an individual, by a group, or by any other controlling private power. -- Franklin D. Roosevelt --

enhydra lutris's picture

are painfully common, you'll find it everywhere, including right here.

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That, in its essence, is fascism--ownership of government by an individual, by a group, or by any other controlling private power. -- Franklin D. Roosevelt --

elenacarlena's picture

them. I've noticed a certain blindness to their own flaws Over There lately, usually accompanied by extreme defensiveness.

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Please check out Pet Vet Help, consider joining us to help pets, and follow me @ElenaCarlena on Twitter! Thank you.

Alphalop's picture

linking to in a thread when someone uses one.

YourLogicalFallicyis:

It's a great resource for those that engage in debate.

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"I used to vote Republican & Democrat, I also used to shit my pants. Eventually I got smart enough to stop doing both things." -Me

enhydra lutris's picture

stating "the name of that fallacy is argumentum ...".

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That, in its essence, is fascism--ownership of government by an individual, by a group, or by any other controlling private power. -- Franklin D. Roosevelt --

here -- who confuse "insult" with "ad hominem".

This is not ad hominem: "Your argument is stupid and you are an evil pig for making it."

This is ad hominem: "You are an evil pig, and therefore your argument is stupid."

Insults are often accurate and valid. Ad hominems are never valid -- an argument stands on its own merits, regardless of the virtues or vices of the person making the argument.

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The earth is a multibillion-year-old sphere.
The Nazis killed millions of Jews.
On 9/11/01 a Boeing 757 (AA77) flew into the Pentagon.
AGCC is happening.
If you cannot accept these facts, I cannot fake an interest in any of your opinions.

Not Henry Kissinger's picture

is another fallacy you see all the time.

Firstly, the claim itself is usually wrong, and typically stems from someone with a very restricted notion of what actually constitutes evidence.

Example: "There's no evidence that Seddique Mateen was invited to the Hilary rally."

False: the picture of him sitting in the VIP section behind Hillary is itself evidence that he was invited.

Secondly, even if there truly is no evidence, the logical fallacy is that an absence of evidence equates to evidence of absence.

I guess you'd call it a corollary of Argumentum Ad Ignorantiam.

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The current working assumption appears to be that our Shroedinger's Cat system is still alive. But what if we all suspect it's not, and the real problem is we just can't bring ourselves to open the box?