the most frequently encountered logical fallacies-rv

7/28/2019 The Most Frequently Encountered Logical Fallacies-Rv

http://slidepdf.com/reader/full/the-most-frequently-encountered-logical-fallacies-rv 1/22

Introduction to Argument

Structure

Whether we are consciously aware of it or not, our arguments all

follow a certain basic structure. They begin with one or more

premises, which are the facts that the argument takes for granted

as the starting point. Then a principle of logic is applied in order

to come to a conclusion. This structure is often illustrated

symbolically with the following example:

Premise 1: If A = B, Premise 2: and B = C Logical connection:

Then (apply principle of equivalence) Conclusion: A = C

In order for an argument to be considered valid the logical form

of the argument must be valid as well. It must work in a valid

way. A valid argument is one in which, if the premises are true,

then the conclusion must be true also. However, if one or more premise is false then a valid logical argument may still lead to a

false conclusion. A sound argument is one in which the logic is

valid and the premises are true, in which case the conclusion

must be true.

Also it is important to note that an argument may use wrong

information, or faulty logic to reach a conclusion that happens to be true. An invalid or unsound argument does not necessarily

prove the conclusion false. Demonstrating that an argument is

not valid or not sound, however, removes it as support for the

truth of the conclusion. It means that the conclusion is not

The Most Frequently Encountered Logical Fallacies



necessarily true because it is not supported by the argument

which is faulty.

Breaking down an argument into its components is a very usefulexercise, for it enables us to examine both our own arguments

and those of others and critically analyze them for validity. This

is an excellent way of sharpening one’s thinking, avoiding biases

and making effective arguments.

Examine your Premises

As stated above, in order for an argument to be sound all of its

premises must be true. Often, different people come to different

conclusions because they are starting with different premises.

So examining all the premises of each argument is a good place

to start.

There are three types of potential problems with premises. The

first, and most obvious, is that a premise can be wrong. If oneargues, for example, that evolutionary theory is false because

there are no transitional fossils, that argument is unsound

because the premise no transitional fossils is false. In fact there

are copious transitional fossils.

Another type of premise error occurs when one or more

premises is an unwarranted assumption. The premise may or may not be true, but it has not been established sufficiently to

serve as a premise for an argument. Identifying all the

assumptions upon which an argument is dependent is often the

most critical step in analyzing an argument. Frequently,




different conclusions are arrived at because of differing

assumptions.

Often people will choose the assumptions that best fit theconclusion they prefer. In fact, psychological experiments show

that most people start with conclusions they desire, then reverse

engineer arguments to support them, a process called

rationalization.

One way to resolve the problem of using assumptions as

premises is to carefully identify and disclose those assumptions

up front. Such arguments are often called “hypothetical,” or

prefaced with the statement “Let’s assume for the sake of

argument”. If two people examine their arguments and realize

they are using different assumptions as premises, then at least

they can “agree to disagree.” They will realize that their

disagreement cannot be resolved until more information is

available to clarify which assumptions are more likely to be

correct.

The third type of premise difficulty is the most insidious: the

hidden premise. I have seen this listed as a logical fallacy called

the unstated major premise, but it is more accurate to consider it

here. Obviously, if a disagreement is based upon a hidden

premise, then the disagreement will be irresolvable. So when

coming to an impasse in resolving differences, it is a good ideato go back and see if there are any implied premises that have

not been addressed.




Let’s go back to the transitional fossil example again. Why is it

that scientists believe we have many transitional fossils and

creationists or intelligent design proponents believe that we do

not? This would seem to be a straightforward factual claimeasily resolvable by checking the evidence. Sometimes

creationists are simply ignorant of the evidence or are being

intellectually dishonest. However, the more sophisticated are

fully aware of the fossil evidence and use a hidden premise to

deny the existence of transitional fossils.

When a paleontologist speaks of “transitional” fossils, they are

referring to species that occupy a space morphologically

between two known species. This may be a common ancestor,

in which case the transitional fossil will be more ancient than

both descendant species; or it can be temporally between two

species, the descendant of one and the ancestor of the other. But

in reality we often do not know if the transitional species is an

actual ancestor or just closely related to the true ancestor.

Because evolution is a bushy process, and not linear, most of thespecimens we find will lie on an evolutionary side branch (an

uncle rather than a parent). But if they fill a morphological gap

in known species, they provide evidence of an evolutionary

connection, and therefore qualify as transitional. For example,

archaeopteryx may not be on the direct path to modern birds, but

clearly they occupy a space that is transitional between therapod

dinosaurs and modern birds and one of their close relatives is adirect ancestor to modern birds.

When those who deny evolution say there are no transitional

fossils to support evolutionary changes, their unstated major




premise is that they are employing a different definition of

transitional than is generally accepted among scientists. They

typically define transitional as some impossible monster with

half-formed and useless structures or they may definetransitional as only those fossils for which there is independent

proof of it being a true ancestor, rather than simply closely

related to a direct ancestor. This sets an impossible standard!

Another hidden premise in their argument is the notion of how

many transitional fossils there should be in the fossil record. An

arbitrarily high number can be established to claim that there are

not enough.

Introduction to Logical Fallacies

Even when all of the premises of an argument are reliably true,

the argument may still be invalid if the logic employed is not

legitimate or incorporates a so-called logical fallacy. The human

brain is a marvelous machine with capabilities that still

outperform the most powerful of super computers. Our brainshowever, do not appear to have evolved specifically for precise

logic. There are many common logical pitfalls that our minds

tend to fall into, unless we are consciously aware of these

pitfalls and make efforts to avoid them.

Heuristics

Humans also tend to use logical short-cuts, called heuristics.

These are thought processes that are not strictly valid in their

logic, but are true most of the time and therefore are a useful




rule-of-thumb as to what is likely to be true. But they may get us

into trouble when they substitute for valid logic.

Also because, as stated above, there is a tendency to start withdesired conclusions and then construct arguments to support

them, many people will happily draw upon logical fallacies to

make their arguments. In fact, if a conclusion is not true one

they must either employ a false premise or a logical fallacy in

order to construct an argument that leads to that conclusion.

Remember, a sound argument (one with true premises and valid

logic) cannot lead to a false conclusion. So in order to avoid

using logical fallacies to construct invalid arguments, we need to

understand how to identify fallacious logic.

Below I will list the most common logical fallacies, with

examples of each.

On the Internet, I have found many lists of logical fallacies, and

they tend to differ along the “lumper vs splitter” spectrum.Many fallacies are really just specific subtypes of a more general

fallacy. They are useful because they help us be aware of the

many varieties of faulty arguments. Here I have attempted a

condensation by listing the main types of fallacies and giving

examples of subtypes where appropriate.

Although this article began as a brief list of logical fallacies, ithas been expanded for your information, and will likely continue

to grow.




Ad hominem

An ad hominem argument is any that attempts to counter

another’s claims or conclusions by attacking the person, rather than addressing the argument itself. True believers will often

commit this fallacy by countering the arguments of skeptics by

stating that skeptics are closed minded. Skeptics, on the other

hand, may fall into the trap of dismissing the claims of UFO

believers by stating that people who believe in UFO’s are crazy

or stupid.

A common form of this fallacy is also frequently present in the

arguments of conspiracy theorists (who often rely heavily on

post-hoc reasoning). For example, they may argue that the

government must be lying because they are corrupt. They often

start with specific examples and then over generalize or they

may start with general or frequent examples and apply them

wrongly to specific cases.

It should be noted that simply calling someone a name or

otherwise making an ad hominem attack is not in itself a logical

fallacy. It is only a fallacy to claim that an argument is wrong

because of a negative attribute of someone making the

argument. (i.e. “George is a jerk.” is not a fallacy. “George is

wrong because he is a jerk.” is a logical fallacy.)

The term “poisoning the well” also refers to a form of ad

hominem fallacy. This is an attempt to discredit the argument of

another by implying that they possess an unsavory trait, or that

they are affiliated with other beliefs or people that are wrong or




unpopular. A common form of this also has its own name –

Godwin’s Law or the reductio ad Hitlerum. This refers to an

attempt at poisoning the well by drawing an analogy between

another’s position and Hitler or the Nazis.

We might get into difficulty when we try to give or take advice

regarding an individual or organization. For example, “George

has a history of lying, cheating, using drugs and dishonest

business practices. Therefore be careful when doing business

with George”.

Ad ignorantiam

The argument from ignorance basically states that a specific

belief is true because we don’t know that it isn’t true. Defenders

of extrasensory perception, for example, will often emphasize

how much we do not know about the human brain. It is

therefore possible, they argue, that the brain may be capable of

transmitting or receiving at a distance. This may or may not betrue, but this is a poor supporting argument.

UFO proponents are probably the most frequent violators of this

fallacy. Almost all UFO eyewitness evidence is ultimately an

argument from ignorance. Lights or objects sighted in the sky

are unknown, and therefore they are alien spacecraft.

Intelligent design is almost entirely based upon this fallacy. The

core argument for intelligent design is that there are biological

structures that have not been well explained by evolution,




therefore a powerful intelligent designer must have created

them.

In order to make a positive claim, however, positive evidencefor the specific claim must be presented. The absence of another

explanation only means that we do not know, it really does not

mean we get to make up a specific explanation and substitute it

for observed facts.

Argument from Authority/Appeal to Authority

The basic structure of such arguments is as follows: Professor X

believes A, Professor X speaks from authority, therefore A is

true. Often this argument is implied by emphasizing the many

years of experience, or the formal degrees held by the individual

making a specific claim. The converse of this argument is

sometimes used, that someone does not possess authority, and

therefore their claims must be false. (This may also be

considered an ad-hominen logical fallacy – see below.)

In practice this can be a complex logical fallacy to deal with. It

is legitimate to consider the training and experience of an

individual when examining their assessment of a particular

claim. Also, a consensus of scientific opinion does carry some

legitimate authority. But it is still possible for highly educated

individuals, and a broad consensus to be wrong. Speaking fromauthority does not make a claim true.

This logical fallacy crops up in more subtle ways also. For

example, UFO proponents have argued that UFO sightings by




airline pilots should be given special weight because pilots are

trained observers, are reliable characters and are trained not to

panic in emergencies. In essence, they are arguing that we

should trust the pilot’s authority as an eye witness.

There are many subtypes of the argument from authority,

essentially referring to the implied source of authority. A

common example is the argument ad populum, a belief must be

true because it is popular, essentially assuming the authority of

the masses. Another example is the argument from antiquity, a

belief has been around for a long time and therefore must be

true.

Argument from Final Consequences

Such arguments (also called teleological) are based on a reversal

of cause and effect, because they argue that something is caused

by the ultimate effect that it has, or purpose that is serves.

Creationists have argued, for example that evolution must bewrong because if it were true it would lead to immorality,

devalue human life and a disregard for God.

One type of teleological argument is the argument from design.

For example, the universe has all the properties necessary to

support life, therefore it was designed specifically to support life

and therefore had a designer.

Argument from Personal Incredulity




I cannot explain or understand this, therefore it cannot be true.

Creationists are fond of arguing that they cannot imagine the

complexity of life resulting from blind evolution, but that does

not mean life did not evolve.

Begging the Question

The term “begging the question” is often misused to mean

“raises the question”, and common use will likely change or at

least add this new definition. However, the intended meaning is

to assume a conclusion in one’s question. This is similar to

circular reasoning, and an opponent is trying to slip a conclusion

into the premise or question, but it is not the same as circular

reasoning because the question being begged can be a separate

point. Whereas with circular reasoning the premise and

conclusion are the same.

The classic example of begging the question is to ask someone if

they have stopped beating their wife yet. Of course, thequestion assumes that they beat their wife. Do you have your

drinking under control?

In a recent appearance on a TV show an MD was asked the

following question. What are alternative medicine skeptics

(termed “holdouts”) afraid of? This is a double feature of

begging the question. By using the term “holdout” the questionassumes that acceptance is already becoming the majority

position and is inevitable. Also, the questioner begged the

question that skeptics are “afraid”. This also created a straw

man (see below) of the physicians position, which is actually




based on a dedication to reasonable standards of science and

evidence.

Confusing Association with Causation

This is similar to the post-hoc fallacy in that it assumes cause

and effect for two variables simply because they occur together.

This fallacy is often used to give a statistical correlation a causal

interpretation. For example, during the 1990’s both religious

attendance and illegal drug use have been on the rise. It would

be a fallacy to conclude therefore that religious attendance

causes illegal drug use. It is also possible that drug use leads to

an increase in religious attendance, or that both drug use and

religious attendance are increased by a third variable, such as an

increase in societal unrest. It is also possible that both variables

are independent of one another, and it is mere coincidence that

they are both increasing at the same time.

This fallacy, however, has a tendency to be abused, or appliedinappropriately, to deny all statistical evidence. In fact this

constitutes a logical fallacy in itself, the denial of causation.

This abuse takes two basic forms. The first is to deny the

significance of correlations that are demonstrated with

prospective controlled data, such as would be acquired during a

clinical experiment. The problem with assuming cause and

effect from mere correlation is not that a causal relationship isimpossible, it’s just that there are other variables that must be

considered and not ruled out a-priori. A controlled trial,

however, by its design attempts to control for as many variables




as possible in order to maximize the probability that a positive

correlation is in fact due to a causation.

Further, even with purely epidemiological or statistical evidenceit is still possible to build a strong scientific case for a specific

cause. The way to do this is to look at multiple independent

correlations to see if they all point to the same causal

relationship. For example, it was observed that cigarette

smoking correlates with getting lung cancer. The tobacco

industry, invoking the “correlation is not causation” logical

fallacy, argued that this did not prove causation. They offered as

an alternate explanation “factor x”, a third variable that causes

both smoking and lung cancer. But we can make predictions

based upon the smoking causes cancer hypothesis. If this is the

correct causal relationship, then duration of smoking should

correlate with cancer risk, quitting smoking should decrease

cancer risk, smoking unfiltered cigarettes should have a higher

cancer risk than filtered cigarettes, etc. If all of these

correlations turn out to be true (which they are), then we can point to the smoking causes cancer hypothesis as the most likely

possible causal relationship and it is not a logical fallacy to

conclude from this evidence that smoking probably causes lung

cancer.

Confusing the Currently Unexplained with Unexplainable

Because we do not currently have an adequate explanation for a

phenomenon does not mean that it is forever unexplainable, or

that it therefore defies the laws of nature or requires a

paranormal explanation. An example of this is the "God of the




Gaps" strategy of creationists that whatever we cannot currently

explain is unexplainable and was therefore an act of god.

False Analogy

Analogies are very useful as they allow us to draw lessons from

the familiar and apply them to the unfamiliar. “Life is like a box

of chocolate, you never know what you’re going to get”.

A false analogy is an argument based upon an assumed

similarity between two things, people or situations when in fact

the two things being compared are not similar in the manner

invoked. Saying that the probability of a complex organism

evolving by chance is the same as a tornado ripping through a

junkyard and creating a 747 by chance is a false analogy.

Evolution does not work by chance but is the non-random

accumulation of favorable changes.

Creationists also make the analogy between life and your home,invoking the notion of thermodynamics or entropy. Over time

your home will become messy, and things will start to break

down. The house does not spontaneously become more clean or

in better repair.

The false analogy here is that a home is an inanimate collection

of objects. Whereas a living system uses energy to grow andreproduce. The addition of energy to a living system allows for

a local reduction in entropy and for evolution to happen.




inheritance). This fallacy assumes that something’s current

utility is dictated by and constrained by its historical utility. This

is easily demonstrated with word usage. A words current use

may be entirely unrelated to its etymological origins. For example, if I use the term “sunset” or “sunrise” I am not

implying belief in a geocentric cosmology in which the sun

revolves about the Earth and literally “rises” and “sets.”

Inconsistency

Applying criteria or rules to one belief, claim, argument, or

position but not to others. For example, some consumer

advocates argue that we need stronger regulation of prescription

drugs to ensure their safety and effectiveness, but at the same

time argue that medicinal herbs should be sold with no

regulation for either safety or effectiveness.

No True Scotsman

This fallacy is a form of circular reasoning, in that it attempts to

include a conclusion about something in the very definition of

the word itself. It is therefore also a semantic argument.

The term comes from the example: If Connor claims that all

Scotsman are brave, and you provide a counter example of a

Scotsman who is clearly a coward, Connor might respond,"Well, then, he's no true Scotsman." In essence Connor claims

that all Scotsman are brave by including bravery in the

definition of what it is to be a Scotsman. This argument does not




establish facts or new information, and is limited to Connors

definition of the word, "Scotsman."

Non-Sequitur

In Latin this term translates to "doesn't follow". This refers to an

argument in which the conclusion does not necessarily follow

from the premises. In other words, a logical connection is

implied where none exists.

Post-hoc ergo propter hoc

This fallacy follows the basic format of: A preceded B, therefore

A caused B, and therefore assumes cause and effect for two

events just because they are temporally related (the latin

translates to "after this, therefore because of this").

Reductio ad absurdum

In formal logic, the reductio ad absurdum is a legitimate

argument. It follows the form that if the premises are assumed to

be true it necessarily leads to an absurd (false) conclusion and

therefore one or more premises must be false. The term is now

often used to refer to the abuse of this style of argument, by

stretching the logic in order to force an absurd conclusion. For

example a UFO enthusiast once argued that if I am skepticalabout the existence of alien visitors, I must also be skeptical of

the existence of the Great Wall of China, since I have not

personally seen either. This is a false reductio ad absurdum

because he is ignoring evidence other than personal eyewitness




evidence, and also logical inference. In short, being skeptical of

UFOs does not require rejecting the existence of the Great Wall.

Slippery Slope

This logical fallacy is the argument that a position is not

consistent or tenable because accepting the position means that

the extreme of the position must also be accepted. But moderate

positions do not necessarily lead down the slippery slope to the

extreme.

Special pleading, or ad-hoc reasoning

This is a subtle fallacy which is often difficult to recognize. In

essence, it is the arbitrary introduction of new elements into an

argument in order to fix them so that they appear valid. A goodexample of this is the ad-hoc dismissal of negative test results.

This fallacy is often taken to ridiculous extremes, and more and

more bizarre ad hoc elements are added to explain experimental

failures or logical inconsistencies. Experimentalists need to be

especially careful of this problem, especially when surrogate

endpoints are used. Experimental design is very important even

in fields that seem straight forward such as chemistry. Politicaland economic arguments are often predicated on ad-hoc

reasoning

Straw Man




A straw man argument attempts to counter a position by

attacking a different position, usually one that is easier to

counter. The arguer invents a caricature of his opponent’s position, a “straw man” that is easily refuted, but not the

position that his opponent actually holds.

For example, defenders of alternative medicine often argue that

skeptics refuse to accept their claims because they conflict with

their world-view. If “Western” science cannot explain how a

treatment works, then it is dismissed out-of-hand. If you read

skeptical treatment of so-called “alternative” modalities,

however, you will find the skeptical position much more

nuanced than that.

Claims are not a-priori dismissed because they are not currently

explained by science. Rather, in some cases like homeopathy

there is a vast body of scientific knowledge that says that

homeopathy is not possible. Having an unknown mechanism isnot the same thing as demonstrably impossible (at least as best

as modern science can tell). Skeptical treatments of homeopathy

often thoroughly review the clinical evidence. Even when the

question of mechanism is put aside, the evidence shows that for

the most part strictly homeopathic remedies are

indistinguishable from placebo. This does not mean that

Homeopathic practitioners have not made valuable observationsand contributions, just that there is no real scientific basis to the

core premise of their therapeutic model.

Tautology




Tautology in formal logic refers to a statement that must be true

in every interpretation by its very construction. In rhetorical

logic, it is an argument that utilizes circular reasoning, whichmeans that the conclusion is also its own premise. Typically the

premise is simply restated in the conclusion, without adding

additional information or clarification. The structure of such

arguments is A=B therefore A=B, although the premise and

conclusion might be formulated differently so it is not

immediately apparent as such. For example, saying that

therapeutic touch works because it manipulates the life force is a

tautology because the definition of therapeutic touch is the

alleged manipulation of the life force.

The Fallacy Fallacy

As I mentioned near the beginning of this article, just because

someone invokes an unsound argument for a conclusion, that

does not necessarily mean the conclusion is false. A conclusionmay happen to be true even if an argument used to support is is

not sound. For example I may argue, Clinton is a Democrat

because the sky is blue, which is an obvious non-sequitur.

Nevertheless the conclusion that Clinton is a Democrat is still

true.

Related to this, and common in the comments sections of blogs,is the position that because some random person on the internet

is unable to defend a position well, that the position is therefore

false. All that has really been demonstrated is that the one

person in question cannot adequately defend their position.




This is especially relevant when the question is highly scientific,

technical or requires specialized knowledge. A non-expert likely

does not have the knowledge at their fingertips to counter anelaborate, but unscientific argument against an accepted science.

“If you (a lay person) cannot explain to me,” the argument

frequently goes, “exactly how this science works, then it is

false.”

Such explanations are often better handled by actual experts.

And, in fact, intellectual honesty requires that at least an attempt

should be made to find the best evidence and arguments for a

position, articulated by those with recognized expertise, and then

account for those arguments before a claim is dismissed. It is

intellectually dishonest for those who demand such an

explanation to become impatient with the detailed explanation

that follows.

The Moving Goal/Moving the Goal

A method of denial that arbitrarily moves the criteria for “proof”

or acceptance out of range of whatever evidence currently exists.

If new evidence comes to light meeting the prior criteria, the

goal is pushed further back, thus keeping it out of range of the

new evidence. Sometimes impossible criteria are set up at the

start, thereby moving the goal impossibly out of range for the purpose of denying an undesirable conclusion.

Tu quoque




Literally, you too. This is an attempt to justify wrong action

because someone else also does it. "My evidence may be

invalid, but so is yours."

Logical Fallacies and Political Persuasion

The study of the use of fallacies in the speech of politicians and

salesmen is in itself an important area of discussion and comes

under the heading of the “Art of Persuasion”. This subject goes

back to ancient times and was well discussed by the Romans. It

remains an important area of study today especially with the

expanded ambient nature of persuasive media.


the most frequently encountered logical fallacies-rv

Documents