BAD REASONING

Beware of these invalid argument methods in science and politics.


FALLACIES OF RELEVANCE
The following invalid arguments are attempts to insert irrelevant material into a debate.
NAME DESCRIPTION EXAMPLE
Appeal to force
Argumentum ad baculum
A threat to use force to win the argument, including war, terrorism, battery, lobbying, strikes, or disruptions. "If you won't pass our law, we will plant explosives when and where you least expect them."
Abuse of power
Argumentum ad baculum
The use of power to win the argument by silencing opponents, or by refusing to let them present their argument. "I rule that your case is out of order, and shall not be presented in these chambers."
Abuse of person
Argumentum ad hominem
This is name-calling or the use of pejoratives and derogatory terms to discredit an argument. "You are a homophobic bigot if you believe that homosexual acts are defined by the Bible to be sins."
Genetic fallacy
Argumentum ad hominem
This is calling an argument not trustworthy because of genetic, ethnic or geographic origin. "You can't trust products made in eastern Asia."
Circumstance
Argumentum ad hominem
This is the use of the expected properties or behaviors of various groups as standards. "Christians are not ever supposed to discriminate against anyone for any reason."
Absence of evidence
Argumentum non indicium
This is making any claim from the fact that no evidence can be found where evidence should be found. "It must have been aliens. Only space aliens could have the ability to not leave any trace that they were here."
Lack of evidence
Argumentum non indicium
This is attempting to wrongly say that something not proved false is true or that something not proved true is false. "Because there is no proof that UFOs are not alien spaceships, they are alien spaceships."
Argument from ignorance
Argumentum ad ignorantium
This is attempting to wrongly shift the burden of proof from the claim maker to another party in the argument. "UFOs are alien spaceships until YOU prove that UFOs are not alien spaceships."
Argument for pity
Argumentum ad misericordiam
This is an attempt to make the outcome of the argument depend on the emotion of pity, rather than logic. "I don't care who's at fault. Only the manufacturer of the gun has the money to pay for his injuries."
NAME DESCRIPTION EXAMPLE
Adverse consequences
Argumentum ad misericordiam
This is an attempt to make the argument depend on possible bad results of a course of action, rather than logic. "If we don't stop global warming, millions of species will become extinct."
Personal incredulity
Argumentum ad incredundus
This is an attempt to make the argument seem incredible because the speaker can't believe it could be true. "I can't believe that global warming will make millions of species will become extinct, so it can't be true."
Appeal to the public
Argumentum ad populum
This is using the opinion of the public to sway a decision without changing the truth. "Write the Senate and tell them not to impeach President Clinton, because he is too popular."
Bandwagon effect
Argumentum ad populum
This is saying that everyone does or believes this without changing the truth. "We should stop climate change because everyone wants it stopped."
Appeal to patriotism
Argumentum ad populum
This is saying that your argument goes against your country without changing the truth. "If you favor gun rights, you are hurting the entire nation."
Appeal to snobbery
Argumentum ad populum
This is using the opinion of the best people to sway a decision without changing the truth. "The most prestigious scientists all agree that climate change is real and so should the best citizens."
Appeal to religion
Argumentum ad populum
This is using a religious belief to sway a decision without changing the truth. "This is not allowed by several religions, so we must not do it."
Appeal to authority
Argumentum ad verecundiam
This is citing the testimonial statements of a self-proclaimed expert, but without any data or proof. "My expert says that global warming is happening. Here's his testimonial statement to tell you so."
Improper authority
Argumentum ad verecundiam
This is citing the testimonial statements of an authority without any supporting data or proof. "My expert on photography says that global warming is happening."
NAME DESCRIPTION EXAMPLE
Biased authority
Argumentum ad verecundiam
This is citing the testimonial statements of an authority that has bias without any supporting data or proof. "My expert wants global warming stopped at any cost. Here's his testimonial statement to tell you so."
Appeal to tradition
Argumentum ad antiquatiam
This is citing something because it has always been true or has been done. "My expert says that the climate has always remained the same, so there is no reason to believe that global warming is happening."
Appeal to hypocricy
Tu quoque
This is citing the failure of the person making the argument to act according to its conclusions. "If you believe global warming is real, why are you traveling everywhere by private jet?"
Accident
Argumentum ad casus
This is using an exception to a general rule, a special case, or an absurdity as the argument. "Using the word seize as an example, the general spelling rule should be that E always goes before I."
Converse accident
Argumentum non casus
This is an attempt to make a general rule vague enough that it would fit all possible cases. "All UFO sightings are caused by misinterpretations of known objects or phenomena."
False cause
Non causa pro causa
This is assigning as the cause of an effect something that occurred only coincidentally. "Rickets appears in certain families, but not others. Therefore it must be a hereditary disease."
Begging the question
Petitio Principii
This is searching for premises to use to prove the conclusion you want to prove to be true, whether or not it is true. "Homosexuality must be hereditary, because homosexuals can't change the way they must behave."
Circular argument
Petitio Principii
This is using a form of the conclusion as one of the premises to prove the conclusion you want to prove to be true. "Homosexuality must be hereditary, because homosexuality can be an unchallenged civil right only if it is hereditary."
Complex question
Argumentum ad multiplexium
This is using an implication associated with the fact that the question was asked to sway an argument. "Have you committed any crimes since you were released from jail twenty five years ago?"
NAME DESCRIPTION EXAMPLE
Irrelevant conclusion
Ignoratio Elenchi
This is forming a conclusion that is unrelated to the arguments already presented. "You are guilty of the crime of murder, because we all know that murder is a fatal crime."
Red Herring
Ignoratio Elenchi
This is forming a conclusion based on something unrelated to the argument. "This man is guilty because he was running down the street after the crime occurred."
Illogical conclusion
Non Sequitur
This is a conclusion that does not logically follow from the provided premises or argument. "Because the weather got hotter, global warming is occurring."
Prestige jargon
Argumentum ad perplexus
This is using big words or technical words that most people don't know to confuse the issue. "My opponent is a homo-sapiens, and regularly engages in monogamous heterosexual activity in matrimony."
Affirming the consequent
Post hoc ergo propter hoc
This is claiming that a given cause is present because some of the expected effects of that cause are present. "Because the icecaps are melting, we must have global warming caused by the activities of man."
Denying the antecedent
Non propter hoc ergo non post hoc
This is claiming that a given effect is not present because a known cause of the effect is not present. "You can't be seeing something up there in the sky, because there are no blips there on the RADAR screen."
Process of elimination
Argumentum ad amotio
This is claiming a certain possibility is true after eliminating all of the other possibilities the speaker can think of. "It's not a bird. It's not a plane. It can't be Superman. Therefore, it must be an alien spaceship."
False dilemma
Argumentum ad amotio
This is claiming that only two possibilities exist when in fact more possibilities can exist. "Either global warming is not happening or humans are causing global warming."
Contradicting premises
contraria sunt
This is when two premises contradict each other. "The politician is smart and he does not think."
NAME DESCRIPTION EXAMPLE
Repetition of premise
Argumentum ad nauseam
This is repeating a false or unproved premise so often that most people think that it is true. "Homosexuality is genetic. Evolution is a scientific fact. Homosexuality is genetic. Evolution is a scientific fact."
Using false information
Argumentum ad mendacium
This is making a claim that is supported by falsified information or information that is known to be biased or tainted. "Cyclamates cause cancer." (Fumigators accidentally killed the lab rats. A student faked results to get his grade.)
Culling the information
Argumentum ad electio
This is filtering out and throwing away as "bad data" any information that does not fit the wanted theory. The Union of Concerned Scientists leak showed they threw away most of their data to be able to prove their case.
Using beliefs as facts
Argumentum ad opinio
This is making a claim supported by a
general belief, rather than by the
known facts.
"Everyone knows there was a second
gunman in the 1963 John F. Kennedy
assassination."
Hasty Conclusion
dicto simplata
This is concluding something without taking the time to gather all of the facts. "Wow! Aliens must have done this."
Everything has a cause
omnia causa fiunt
This is the false premise that everything is caused by something else. "Everything has a cause. So what caused the first thing?"
Special Pleading
nostra speciali casu
This is the false premise that the case presented is special, not ordinary. "You have to give us special rights because we are not ordinary people."
Undistributed middle
non distributio medii
This is a fallacy where the middle term (the one not in the conclusion) is in the same case in both premises. "1. All engineers have degrees;
2. Jerry has a degree;
∴ Jerry is an engineer."

FALLACIES OF AMBIGUITY
The following invalid arguments are attempts to insert ambiguous material into a debate.
NAME DESCRIPTION EXAMPLE
Equivocation
Dubius mutatio
This is using two different meanings of the same word or phrase in different premises in an argument. 1. "Squirrels eat nuts."
2. "You are a certifiable nut."
∴ "Stay away from squirrels!"
Amphiboly
Amphibolium mutatio
This is using a phrase that can have two different meanings, giving the argument two different meanings. "The public official wrote that man a citation for the events he caused to happen the previous week."
Accent shift
Vox mutatio
This is giving a different meaning to a sentence by changing which word or syllable gets the accent. "He saw that gasoline can explode."
(Was this an actual event, or a lesson he received in chemistry class?)
Composition
Argumentum ad compositio
This is assigning the properties of a single individual or component to the entire group or class. 1. "A policeman committed a rape."
∴ "All policemen are likely to
    commit rapes."
Division
Argumentum ad partiri
This is assigning the properties of an entire group to a single individual or component. 1. "All Christians take communion."
∴ "You, as an individual Christian, must
    have taken communion at least once."
Obfuscation
Argumentum obfuscarius
Presenting information in a way that confuses most people or hides the truth from them. Using one or more of the many tricks used to make misleading charts intended to bias an argument.
Vague prediction
Argumentum incertus
Making predictions that could be satisfied by a large number of differing events. "If you walk under a ladder, spill salt, break a mirror, or see a black cat, you will have bad luck."
Vague analogy
Argumentum incertus
Making comparisons based on a faulty analogy between two different things. "Because religious beliefs are like fairy tales, religious beliefs must be fairy tales."
NAME DESCRIPTION EXAMPLE
Temporal amphiboly
Amphibolium temporum
Reading into a document meanings of words that were not yet coined when the document was originally written. "The US Constitution phrase, 'general welfare of the United States,' requires welfare payments for the poor."
Misleading statistic
Statisticum mutatio
Using a statistic in a misleading way to form a wrong conclusion. "Because 40% of sick days were Mondays or Fridays, workers misused sick time for 3-day weekends.
Note: 40% of 5 workdays is 2 days."
.
TESTS TO APPLY TO CLAIMS
Use these to test for attempts to insert irrelevant material into a debate.
NAME DESCRIPTION EXAMPLE
Relevance Is it relevant to the debate in progress?
Is what is being presented germane to the argument being presented?
The murder weapon is relevant to a murder trial. The color of the prosecutor's eyes is not.
Testability Is the argument testable? Can logical, evidentiary, or scientific tests be applied to the argument? We have proved that natural selection occurs. We can't test whether evolution caused the origin of life on earth.
Compatibility Is it compatible with what we already know to be true? Or does it require what we already know to be changed? Perpetual motion as a power source is not compatible with current knowledge of sources of energy.
Prediction or explanation Does it make observable predictions or explain existing observations? Or is neither of these applicable? The theory of relativity explains the changes in lifetimes of particles with speed, but not why jokes are funny.
Simplicity Is it simple? Does it require a minimum of assumptions and special effects? Or is it too complicated? Fire balloons are a simple explanation for UFO sightings. Alien spaceship theories are not as simple.
Logic Is it based on sound logical thought?
Emotional claims are worthless in most arguments.
The sad story of polar bear habitats is not a valid premise in an argument on the reality of global warming.
Composure Is the person presenting the argument calm? An angry or fearful presentation usually means illogical thinking. Those worried about dire consequences of an outcome are usually panicky or emotional.

VALID ARGUMENT MODES
Unlike the erroneous methods above, these are valid:
NAME DESCRIPTION EXAMPLE
Affirming the antecedent
Modus Ponens
The presence of the cause proves the presence of the effect.
P→Q; P; ∴ Q
1. Water dissolves salt;
2. Water got into the salt;
∴ The salt dissolved.
Denying the consequent
Modus Tollens
The absence of the effect proves the absence of the cause.
P→Q; ~Q; ∴ ~P
1. Water dissolves salt;
2. The salt did not dissolve;
∴ The liquid is not water.
Overlapping conditionals
Hypothetical syllogism
The effect from one cause is the cause of another effect.
P→Q; Q→R; ∴ P→R
1. Light attracts bugs;
2. Bugs attract fish;
∴ Light will bring fish.
Cancellation of disjunct
Disjunctive syllogism
Proving one item is present by disproving the only other possible item.
P∨Q; ~P; ∴ Q
1. A cabbage must be green or purple;
2. My cabbage is not purple.
∴ My cabbage must be green.
Dilemma
Constructive dilemma
Either of two causes imply either of two effects
P→Q; R→S; P∨R; ∴ Q∨S
1. Roses are red;   2. Bluebells are blue;
3. We have roses or bluebells;
∴ The flowers are red or blue.
Absorption
Absorption of Antecedent
The cause implies both the cause and the effect.
P→Q; ∴ P→(P&Q)
1. Sapphires are blue;
∴ Sapphires are both sapphires and blue.
Exportation
Exportation of Antecedent
If two things together cause an effect, then one makes the other cause it.
(P&Q)→R; ∴ P→(Q→P)
1. Boys and girls act silly when together;
∴ The presence of boys implies that
    the girls will act silly.
Simplification
Severance of conjunction
If both are true, then either is true by itself.
P&Q; ∴ P; ∴ Q
1 There are boys and girls present;
∴ Boys are present;
∴ Girls are present.
Conjunction
Conjoining truth
If two items are true separately, they are true together.
P; Q; ∴ P&Q
1. Boys are present;
2. Girls are present;
∴ Boys and girls are present.
NAME DESCRIPTION EXAMPLE
Addition
Disjoining truth
If one item is true, then that item or another item is true.
P; ∴ P∨Q
1. Boys are present;
∴ Boys or girls are present.
    (whether or not girls are present)
Repetition
Reflexive property (for second use)
If the statement is true, then the statement is true.
P = P
1. Sapphires are blue;
∴ Sapphires are blue.
    (duh.)
DeMorgan's laws
Nondistributive complement
Complements are not distributive:
~(P&Q) = ~P∨~Q
~(p∨Q) = ~P&~Q
If neither boys nor girls are present,
then no boys are present and
no girls are present.
Commutation
The commutative laws
P&Q = Q&P
P∨Q = Q∨P
P≡Q = Q≡P
If boys and girls are present,
then girls and boys are present.
(note the order)
Association
The associative laws
The grouping laws:
P&(Q&R) = (P&Q)&R
P∨(Q∨R) = (P∨Q)∨R
If germs are present with ladies and gentlemen,
then germs and ladies are present
with gentlemen.
Distribution
The distributive laws
Distribute conjunction and disjunction
P&(Q∨R) = P&Q∨P&R
P∨Q&R = (P∨Q)&(P∨R)
If germs are present with girls or boys,
then germs and girls or
germs and boys are present.
Double negative
Double negation
Two complements cancel each other.
So a not not is not a not.
~~P = P
If it is not true that people were not there, then people were there.
(Not true that no people were there.)
Implication
Implication of disjunction
If P implies Q, then
P is false or Q is true.
P→Q = ~P∨Q
If roses are red,
then either no roses are present, or
red flowers are present.
Equivalence
Material equivalence
P≡Q = P&Q ∨ ~P&~Q
P≡Q = P&Q ∨ ~(P∨Q)
P≡Q = (P→Q) ∧ (Q→P)
If two claims are equivalent, then
either both are true, or both are false.
Each implies the other.
NAME DESCRIPTION EXAMPLE
Transposition
Transposition of implication
Modus ponens changed to modus tollens.
P→Q = ~Q→~P
If bluebells are blue, then
the flowers that aren't blue are not bluebells.
Tautology
Repetition of premise
The same premise appears twice.
P = P & P
P = P ∨ P
If people are present,
then people are present
and people are present.
Identity
Equivalent forms
Identity values don't change outcome.
P = P&true
P = P∨false
The truth of this statement is
equivalent to the truth of this
statement and truth itself.
Contradiction
Disproof of conjunction
It is asserted that two statements must be true, but one is proved false.
P & Q; ~Q; ∴ false     P & false = false
I have both dimes and quarters,
but I don't have any dimes.
The statement contradicts itself.