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	This is a threat to use force to win the argument, including war, terrorism, battery, lobbying, strikes, disruptions, or casting a vote.	"If you won't pass our law, we will plant bombs when and where you least expect them."
Abuse of power Argumentum ad baculum	This is 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, and the use of pejoratives and derogatory terms.	"You are a bigot if you believe homosexuality is a sin."
Circumstance Argumentum ad hominem	This is the use of the expected behaviors of various groups.	"Christians are not supposed to discriminate."
Argument from ignorance Argumentum ad ignorantium	This is attempting to shift the burden of proof to the other side.	"Until you prove that UFOs are not alien spaceships, we say they are alien spaceships."
Argument for pity Argumentum ad misericordiam	This is an attempt to make the outcome depend on pity, rather than logic.	"I don't care who's at fault. Only the manufacturer has the money to pay for his injuries."
Appeal to the public Argumentum ad populum	This is using public opinion to sway the argument without changing the truth.	"Write the Senate and tell them to not impeach President Clinton."
Appeal to authority Argumentum ad verecundiam	This is citing the testimonial statements of a self-proclaimed expert, but without any data.	"My expert says that global warming is happening. Here's his testimonial statement."
Accident Argumentum ad casus	This is using an exception to a general rule, a special case, or an absurdity.	"Using the word seize as an example, E always goes before I."
NAME	DESCRIPTION	EXAMPLE
Converse accident Argumentum non casus	This is an attempt to make a general rule vague enough to fit all possible cases.	"All UFO sightings are caused by misinterpretations of known objects."
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, therefore it is a hereditary disease."
Begging the question Petitio Principii	This is searching for premises to use to prove what you want to prove.	"Homosexuality must be hereditary, because homosexuals can't change their behavior."
Complex question Argumentum ad multiplexium	This is using an implication associated with the fact that a question was asked.	"Have you committed any crimes since you were released from jail?"
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 murder is a crime."
Prestige jargon Argumentum ad perplexus	This is using big words or technical words which few people know to confuse the issue.	"My opponent is a homo-sapiens, and engages in heterosexual activity."
Affirming the consequent Post hoc ergo propter hoc	This is claiming that a given cause is present because some of the effects of that cause are present.	"Because the icecaps are melting, we must have global warming caused by 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 in the sky, because there are no blips on the RADAR screen."
Process of elimination Argumentum ad amotio	This is claiming a certain possibility is true after eliminating all other possibilities the speaker can think of.	"It's not a bird, a plane, or Superman, so it must be an alien spaceship."
NAME	DESCRIPTION	EXAMPLE
Repetition of premise Argumentum ad nauseam	This is repeating a false or unproved premise so often that most people think it is true.	"Evolution is a scientific fact. Evolution is a scientific fact. Evolution is a scientific fact."
Using false information Argumentum ad mendacium	This is making a claim supported by falsified information or information that is known to be tainted.	"Cyclamates cause cancer." (Fumigators accidentally killed the lab rats. The student faked results to get his grade.)
Culling the information Argumentum ad electio	This is throwing away any information that does not fit the wanted theory as "bad data."	"People want subsidized health care. We have data from every city core neighborhood."
Using beliefs as facts Argumentum ad opinio	This is making a claim supported by a general belief, rather than by known facts.	"Everyone knows there was a second gunman in the John F. Kennedy assassination."
Absence of evidence Argumentum non indicium	This is making any claim from the fact that no evidence can be found.	"It must have been aliens. Only space aliens could have the ability to not leave any trace they were here."

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 different meanings of the same phrase in different premises.	"Squirrels eat nuts. You're a nut. Stay away from squirrels!"
Amphiboly Amphibolium mutatio	This is using a phrase that can have two different meanings in an argument.	"The public official gave that man a citation."
Accent shift Vox mutatio	This is giving a different meaning to a sentence by changing the accent.	"He saw that gasoline can explode." (An event, or a lesson?)
Composition Argumentum ad compositio	Assigning the properties of an individual component to the entire group.	"A policeman committed a rape. So all policemen commit rape."
Division Argumentum ad partiri	This is assigning the properties of an entire group to an individual component.	"You must have taken communion. Christians take communion."
Obfuscation Argumentum obfuscarius	Presenting information in a way that confuses most people or hides the truth.	Using one or more of the many tricks used to make misleading charts.
Vague Prediction Argumentum incertus	Making a prediction that could be satisfied by a large number of differing events.	"If you walk under a ladder, you will have bad luck."
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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?	The murder weapon is relevant to a murder trial.
Testability	Is the argument testable?	We can't test whether evolution was the origin of life on earth.
Compatibility	Is it compatible with what we already know to be true?	Perpetual motion as a power source is not compatible with current knowledge.
Prediction/Explanation	Does it make observable predictions or explain existing observations?	The theory of relativity explains the changes in lifetimes of particles.
Simplicity	Is it simple? Does it require a minimum of assumptions and special effects?	Alien spaceships are not a simple explanation to UFO sightings.
Logic	Is it based on sound logic? Emotional claims are worthless.	The sad story of polar bear habitats is not valid data on the reality of global warming.
Composure	Is the person presenting the argument calm? An angry presentation usually means illogical thinking.	Those worried about the dire consequences of an outcome are usually 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	Water dissolves salt; water got into the salt; thus the salt dissolved.
Denying the consequent Modus Tollens	The absence of the effect proves the absence of the cause. P→Q; ~Q; ∴ ~P	Water dissolves salt; the salt did not dissolve; thus, water was not present.
Overlapping Conditionals Hypothetical syllogism	A chain of cause and effect: P→Q; Q→R; ∴ P→R	Light attracts bugs; bugs attract fish; thus light attracts fish.
Cancellation of disjunct Disjunctive syllogism	Proving one item is present by disproving another of the two possible. P∨Q; ~P; ∴ Q	The cabbage is green or red; It isn't red, so it must be green.
Dilemma Constructive dilemma	Either of two causes imply either of two effects P→Q; R→S; P∨R; ∴ Q∨S	Carnations are pink; Bluebells are blue; We have carnations or bluebells; thus the flowers are pink or blue.
Absorption Absorption of Antecedent	The cause implies both the cause and the effect. P→Q; ∴ P→(P&Q)	Sapphires are blue; thus sapphires are both sapphires and blue.
Exportation Exportation of Antecedent	The conjunction of causes. (P&Q)→R; ∴ P→(Q→P)	Boys and girls act silly when together, thus 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	There are boys and girls present; thus boys are present; thus girls are present.
Conjunction Conjoining truth	If two items are true separately, they are true together. P; Q; ∴ P&Q	Boys are present; girls are present; thus boys and girls are present.
Addition Disjoining truth	If one item is true, then that item or another item is true. P; ∴ P∨Q	Boys are present; thus boys or girls are present.
Repetition Reflexive property (for second use)	If the statement is true, then the statement is true P = P	Sapphires are blue; thus sapphires are blue.
NAME	DESCRIPTION	EXAMPLE
DeMorgan's Laws Nondistributive complement	~(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.
Association The associative 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	P&(Q∨R) = P&Q∨P&R P∨Q&R = (P∨Q)&(P∨R)	If germs are present with girls pr boys, then germs and girls or germs and boys are present.
Double Negative Double negation	~~P = P	If it is not true that people were not there, then people were there.
Implication Implication of disjunction	P→Q = ~P∨Q	If carnations are pink, then either no carnations are present, or pink flowers are present.
Equivalence Material equivalence	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.
Transposition Transposition of implication	P→Q = ~Q→~P	If carnations are pink, the flowers that aren't pink are not carnations.
Tautology Repetition of premise	P = P&P P = P∨P	If people are present, then people are present and people are present.
Identity Equivalent forms	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.