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, and 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."
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."
Argument from ignorance
Argumentum ad ignorantium
This is attempting to wrongly shift the burden of proof to another party in the argument. "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 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."
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."
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."
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."
NAME DESCRIPTION EXAMPLE
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 various 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 ever change the way they must behave."
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?"
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."
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 must be 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."
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."
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."

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."
Temporal Amphiboly
Amphibolium Temporum
Reading into a document some meanings of words that had not yet been coined when the document was originally written. "The US Constitution phrase, 'general welfare of the United States,' requires welfare payments for the poor."
.
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/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 other of two possible items.
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 the effect.
(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.
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.)
NAME DESCRIPTION EXAMPLE
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
Distribution of 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.
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.