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Top Logical Fallacies: Non sequitur A non sequitur (literally, does not follow) is a logical fallacy. Reasoning is said to be non sequitur if the conclusion does not follow from the premises or if a given reason for taking an action is completely irrelevant to taking that action. For example, the police chief’s reasoning was a non sequitur when he defended consulting a psychic “to help investigators crack the case” based on the premise that “we tried everything else and haven’t solved the case.” The fact that the case hadn’t been solved using traditional police methods is irrelevant to whether consulting a psychic is a method that should be used. The error in reasoning should become obvious if we substitute “pick a name randomly out of the phone book to identify the main suspect ” for “consult a psychic.” The fact that you haven’t solved the case using traditional methods provides no support for trying a non-traditional method. To justify trying a non-traditional method, one needs direct evidence that the non-traditional method has some merit. One often finds that non sequitur reasoning given by those trying to justify hiring a psychic or going to an “alternative” therapist is accompanied by another fallacy: the questionable assumption. For example,  ”we had nothing to lose by consulting a psychic” or “I had nothing to lose by going to a homeopath” are questionable claims. You could be losing time and money that could be better spent. Via skepdic

Top Logical Fallacies: Non sequitur

A non sequitur (literally, does not follow) is a logical fallacy. Reasoning is said to be non sequitur if the conclusion does not follow from the premises or if a given reason for taking an action is completely irrelevant to taking that action.

For example, the police chief’s reasoning was a non sequitur when he defended consulting a psychic “to help investigators crack the case” based on the premise that “we tried everything else and haven’t solved the case.”

The fact that the case hadn’t been solved using traditional police methods is irrelevant to whether consulting a psychic is a method that should be used.

The error in reasoning should become obvious if we substitute “pick a name randomly out of the phone book to identify the main suspect ” for “consult a psychic.” The fact that you haven’t solved the case using traditional methods provides no support for trying a non-traditional method. To justify trying a non-traditional method, one needs direct evidence that the non-traditional method has some merit.

One often finds that non sequitur reasoning given by those trying to justify hiring a psychic or going to an “alternative” therapist is accompanied by another fallacy: the questionable assumption. For example,  ”we had nothing to lose by consulting a psychic” or “I had nothing to lose by going to a homeopath” are questionable claims. You could be losing time and money that could be better spent.

Via skepdic

(via bluedogeyes)



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Top Logical Fallacies: False Dichotomy A false dilemma (also called false dichotomy, the either-or fallacy, fallacy of false choice, black-and-white thinking, or the fallacy of exhaustive hypotheses) is a type of logical fallacy that involves a situation in which only two alternatives are considered, when in fact there are additional options (sometimes shades of grey between the extremes). For example, “It wasn’t medicine that cured Ms. X, so it must have been a miracle.” (image via gloomies) False dilemma can arise intentionally, when fallacy is used in an attempt to force a choice (such as, in some contexts, the assertion that “if you are not with us, you are against us”). But the fallacy can also arise simply by accidental omission of additional options rather than by deliberate deception (e.g., “I thought we were friends, but all my friends were at my apartment last night and you weren’t there”). A false dichotomy is typically used in an argument to force your opponent into an extreme position  by making the assumption that there are only two positions. Examples: “If you want better public schools, you have to raise taxes. If you don’t want to raise taxes, you can’t have better schools.” - A third alternative is that you could spend the existing tax money more efficiently. “You’re either part of the solution or part of the problem.” - No room for innocent bystanders here. “If you’re not with us, you’re against us.” - Being neutral is not an option. Forcing to classify people as either “with us” or “against us”, leads to the saying “An enemy of my enemy is my friend.” While they may hate both of you. Black-and-white thinking In psychology, a related phenomenon to the false dilemma is black-and-white thinking. Many people routinely engage in black-and-white thinking, an example of which is someone who labels other people as all good or all bad. via: wikipedia / c2 

Top Logical Fallacies: False Dichotomy

A false dilemma (also called false dichotomy, the either-or fallacy, fallacy of false choice, black-and-white thinking, or the fallacy of exhaustive hypotheses) is a type of logical fallacy that involves a situation in which only two alternatives are considered, when in fact there are additional options (sometimes shades of grey between the extremes).

For example, “It wasn’t medicine that cured Ms. X, so it must have been a miracle.”

(image via gloomies)

False dilemma can arise intentionally, when fallacy is used in an attempt to force a choice (such as, in some contexts, the assertion that “if you are not with us, you are against us”). But the fallacy can also arise simply by accidental omission of additional options rather than by deliberate deception (e.g., “I thought we were friends, but all my friends were at my apartment last night and you weren’t there”).

A false dichotomy is typically used in an argument to force your opponent into an extreme position  by making the assumption that there are only two positions.

Examples:

“If you want better public schools, you have to raise taxes. If you don’t want to raise taxes, you can’t have better schools.” - A third alternative is that you could spend the existing tax money more efficiently.

“You’re either part of the solution or part of the problem.” - No room for innocent bystanders here.

“If you’re not with us, you’re against us.” - Being neutral is not an option.


Forcing to classify people as either “with us” or “against us”, leads to the saying “An enemy of my enemy is my friend.” While they may hate both of you.

Black-and-white thinking

In psychology, a related phenomenon to the false dilemma is black-and-white thinking. Many people routinely engage in black-and-white thinking, an example of which is someone who labels other people as all good or all bad.

via: wikipedia / c2 



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Top Logical Fallacies

Confusing 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 Gapsa” strategy of creationists that whatever we cannot currently explain is unexplainable and was therefore an act of god.

(Source: bluedogeyes)



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Top Logical Fallacies

Negative Proof Fallacy

The negative proof fallacy is where one assumes something is true if it cannot be proven false. It can also happen when one assumes that something is false if it cannot be proven true.

An infinite amount of silly statements might be declared and be completely unprovable, hence we cannot assume validity in the face of unprovability. This is what is known as burden of proof.

A negative proof is a logical fallacy which takes the structure of:

X is true because there is no proof that X is false.

If the only evidence for something’s existence is a lack of evidence for it not existing, then the default position is one of skepticism and not credulity. This type of negative proof is common in proofs of God’s existence or in pseudosciences where it is used to attempt to shift the burden of proof onto the skeptic rather than the proponent of the idea. The burden of proof is on the individual proposing existence, not the one questioning existence.

Retort

A common retort to a negative proof is to reference the existence of the Invisible Pink Unicorn or the Flying Spaghetti Monster as just as valid as the proposed entity of the debate. This is similar to reductio ad absurdum, that taking negative proof as legitimate means can prove practically anything, regardless how absurd.

(via logical-critical-thinking  rationalwiki)

(Source: bluedogeyes)



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No True Scotsman logical fallacy  (via RationalWiki) No True Scotsman is a logical fallacy by which an individual attempts to avoid being associated with an unpleasant act by asserting that no true member of the group they belong to would do such a thing. Instead of acknowledging that some members of a group have undesirable characteristics, the fallacy tries to redefine the group to exclude them. Sentences such as “all members of X have desirable trait Y” then become tautologies, because Y becomes a requirement of membership in X…  Phrases such as “un-American”, “un-Christian” or “inhuman” are widely used in politics and media to distance oneself from a subject, defining them as outside the bounds of what the speaker considers to be truly ‘American’, ‘Christian’ or ‘human’ behaviour. These phrases strongly suggest the No True Scotsman fallacy, since the use, for example of “un-American” to describe specific political activities by some American citizens implies some special definition of “American” beyond mere nationality. With respect to religion, the fallacy is well used, often even overused. Religious apologists will repeatedly try to use the No True Scotsman argument to distance themselves from more extreme or fundamentalist groups but this does not prevent such extremists actually being religious - they themselves would certainly argue otherwise. Moderate Muslim leaders, for example, are well known for declaring Islamic extremists as “not true Muslims” as Islam is a religion of peace. Similarly, moderate Christians, such as those in Europe, sometimes aghast when viewing their right-wing counterparts in the US, immediately declare them “not true Christians”, even though they believe in the same God and get their belief system of it from the same book… Occasionally atheists can be guilty of the fallacy, such as someone hypothetically exclaiming that “true atheists” don’t believe in ghosts or UFOs when such disbeliefs actually have nothing to do with an atheistic philosophy (although they can be linked by concepts of observational evidence and rationalism).

No True Scotsman logical fallacy  (via RationalWiki)

No True Scotsman is a logical fallacy by which an individual attempts to avoid being associated with an unpleasant act by asserting that no true member of the group they belong to would do such a thing. Instead of acknowledging that some members of a group have undesirable characteristics, the fallacy tries to redefine the group to exclude them. Sentences such as “all members of X have desirable trait Y” then become tautologies, because Y becomes a requirement of membership in X… 

Phrases such as “un-American”, “un-Christian” or “inhuman” are widely used in politics and media to distance oneself from a subject, defining them as outside the bounds of what the speaker considers to be truly ‘American’, ‘Christian’ or ‘human’ behaviour. These phrases strongly suggest the No True Scotsman fallacy, since the use, for example of “un-American” to describe specific political activities by some American citizens implies some special definition of “American” beyond mere nationality.

With respect to religion, the fallacy is well used, often even overused. Religious apologists will repeatedly try to use the No True Scotsman argument to distance themselves from more extreme or fundamentalist groups but this does not prevent such extremists actually being religious - they themselves would certainly argue otherwise. Moderate Muslim leaders, for example, are well known for declaring Islamic extremists as “not true Muslims” as Islam is a religion of peace. Similarly, moderate Christians, such as those in Europe, sometimes aghast when viewing their right-wing counterparts in the US, immediately declare them “not true Christians”, even though they believe in the same God and get their belief system of it from the same book…

Occasionally atheists can be guilty of the fallacy, such as someone hypothetically exclaiming that “true atheists” don’t believe in ghosts or UFOs when such disbeliefs actually have nothing to do with an atheistic philosophy (although they can be linked by concepts of observational evidence and rationalism).



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Top Logical Fallacies…

Straw man

A straw man is a component of an argument and is an informal fallacy based on misrepresentation of an opponent’s position. To “attack a straw man” is to create the illusion of having refuted a proposition by substituting it with a superficially similar yet unequivalent proposition (the “straw man”), and refuting it, without ever having actually refuted the original position

Example

Straw man arguments often arise in public debates such as a (hypothetical) prohibition debate:

Person A:

 We should liberalize the laws on beer.

Person B: 

No, any society with unrestricted access to intoxicants loses its work ethic and goes only for immediate gratification.

The proposal was to relax laws on beer. Person B has exaggerated this to a position harder to defend, i.e., “unrestricted access to intoxicants”. This example is also a slippery slope fallacy.

 (via Wikipedia)

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(Source: bluedogeyes)



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Top Logical Fallacies…

Argument from 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 from authority 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 populi – 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.

(via  The Skeptics’ Guide to the Universe)



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