Critical Thinking Project

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*Absent Control, Fallacy of C&P page:

Inferring a correlation (maybe even a causal connection) between A and B, from the premise that some percentage (usually a high one) of instances of A are also instances of B, while failing to compare that percentage against the percentage of non-As which are Bs.

People commonly declare that washing their car enhances the chances of there coming up a rainstorm. "Every time I wash my car, it rains", they say. Well, maybe so, but the question is, how likely is it to rain if they don't wash their car? Checking into the meteorological data may reveal that it rains all the doggone time, whether they wash their car or not-- so much for their causal inference.

*Ad Hominem a.k.a.: Attacking the Person C&P page: 175

A persuasion strategy in which the peddler attempts to defend her own position by pointing out the undesirable associations, personal characteristics, or motives of those who do not accept it.

The impact of the suggestion that "only bad people disagree with me" is often supplemented with an "all good people agree with me", introducing an appeal to diffuse authority. The big (and overlooked) question is, what has their badness or your goodness got to do with the truth of your position? The big (and overlooked) answer typically is "Nothing."

*Affirming the Antecedent a.k.a.: Modus Ponens C&P page: 26, 110

Definition: A common, valid argument form in which the antecedent of a conditional premise is "affirmed" by a second premise, which unconditionally states that antecedent term, and in which the conclusion consists of the consequent term, thus following the pattern:
1) If A, then B.
2) A.
Therefore, B.

*Ambiguity : C&P page: 194-5

Definition: A term in a context is ambiguous if it has more than one relatively distinct meaning in that context 

*ambiguity, crucial : C&P page:

Definition: An ambiguity is a crucial one if, depending on how an ambiguous term is interpreted, in the context of a premise statement, the truth-value of the statement changes between True and False.

*Analogical Reasoning : C&P page: 264-p

Definition: Reasoning that attempts to justify the conclusion that situation X has quality Y, by appeal to a sufficiently similar (analogous) situation X', which is said to have Y or some similar quality Y'.

Comment: Crudely, an argument exemplifying analogical reasoning says "X is like X', and X' has quality Y (or something like it), so X will (probably) have quality Y too. The big question is whether X is so much like X' that it's reasonable to expect their other qualities to be similar too. This key premise is very typically unstated, and even when it is made explicit it is very typically impeach able (i.e. in need of further defense).

*and a.k.a.: but, C&P page:

Definition: A three-letter word in English which combines simple statements into more complex ones, according to the rule that the complex statement is True if both the simpler ones are true, and False if either of the simpler ones are false.

*antecedent : C&P page:

Definition: The "iffy" part of an "if-then" statement.

Comment: "Antecedent" and "consequent", as technical terms, refer only to parts of a conditional statement. Thus there is neither consequent nor antecedent in statements of the form "A or B", and in particular, A is not the antecedent in such a statement.

Not every statement following the word "if" is the antecedent of a conditional. For example, statements of the form "A only if B" translate into the conditional "If A then B", where you can see that actually B represents the consequent statement, not the antecedent.

*Appeal to (Diffuse) Authoritya.k.a.: Diffuse Authority C&P pg: 175

Definition: Defending a claim C by citing, as a premise, the fact someone E says or thinks C, where E's expertise (if any) is not relevant to the issue at hand, even though E may be someone who is famous or admired.

Comment: It's not necessarily fallacious, or irrational, to appeal to the judgment of authorities in support of a given statement. It is seriously irrational, however, to base your acceptance of a statement on the word of someone who doesn't know what they're talking about. For the many further requirements of a rational appeal to authority, refer to our analysis of Testimonial Arguments.

*Appeal to Force a.k.a.: Argumentum Ad Baculum C&P pg:170

Definition: A peddler's strategy to reduce the critical impulses of the propositional consumer by demonstrating or implying that it could dangerous to disagree with the peddler's statements.

Comment: Telling McFnerk "believe me or I'll kill you" rarely makes a believer out of McFnerk. However, killing McFnerk when he refuses to believe you can make a believer out of people who see you do this, since humans have a perverse tendency to worship power. In any event, as critical impulses (if not critics) die out, your propositions have an easier time gaining acceptance.

To classify appeal to force as a fallacy is based on the perception that truth is no respecter of strength. To introduce the issue of power is to introduce an irrelevancy, and thus invite a change of subject. As consumer, you should point out the choice being offered to you, emphasizing that the two issues are unrelated. Then you may decline graciously to deal with the issue of power (or, alternatively, you can beat the tar out of your opponent.) Then re-address the original topic.

*appeal to ignorance C&P page:

Definition: The strategy of seeking to support a statement by pointing out that you (the consumer) can not show that it is false, or even that all attempts to prove it false have consistently failed.

Comment: Peddlers draw various messages from such a fact about their peddled proposition-- sometimes they'll say this proves them right; others that it simply deprives you of any grounds for not agreeing with them, at least until you can show they're mistaken.

The "ignorance" here is the consumer's not knowing (since lacking proof) the statement to be false. The missing premise in the argument is "Either a statement is known to be false, or it's true,"-- plainly, a false dichotomy. In reply, the consumer might point that if her ignorance proved anything, she'd have to accept both "There's a 1000kg boulder on the dark side of the moon" and "There is not a 1000kg boulder on the dark side of the moon."

And how smart would that be?

*Appeal to Pity a.k.a.: Ad Misericordiam C&P page: 170

Definition: Seeking to support a statement by stating or suggesting that some person or creature the consumer cares about (maybe even the peddler) would be hurt or harmed by the consumer's not accepting the truth of the peddler's proposition.

Comment: Note that we're talking about statements and believing them, not actions and performing them. That your action would result in harm to loved ones is a good reason for not doing it. But that your hard-shell fundamentalist grandmother would fall right out of her combat boots if she heard you had accepted the theory of evolution is not a good reason for you to decide that the theory is not true.

*Argument C&P page: 15

Definition: *An argument is a collection of statements in which one or more (known as the premises) are given for the purpose of justifying, or defending as true, another statement (the conclusion).

Comment: "Argument" is a technical term, in the context of logic, and does not imply or presuppose a dialogue or discussion between two individuals, much less an emotionally heated exchange or disagreement. The presenter of an argument may not be fully aware of its structure-- some serious reconstruction may be required, to extract an argument from his initial mishmash of statements. 

*Argumentum Ad Homily C&P page:

Definition: A presentation which attempts to justify or explain some particular action or situation (e.g. losing this football game) by reference to some popular generalization about the way of all things, or the nature of the universe (e.g. "You can't win `em all.")

Comment: Ironically, to traffic in such phrases as "That's how the cookie crumbles," is commonly called being philosophical! Behind the ad populum appeal of the generalization, careful analysis usually discloses a false dichotomy, a slippery slope, or a fallacy of division.

*Begging the Question a.k.a.: Petitio Principii C&P page: 163

Definition: An argument that rests on a premise that is either a restatement of the conclusion or that would would be doubted for the same reason that the conclusion would be doubted. 

*burden of proof, principle of : C&P page:

Definition: A regulatory principle of forensic debate, which assigns the responsibility of defending an assertion to the party that asserts it.

Comment: In other words, the job of proving it's true goes to the guy who claims it's true. In still other words, your just saying it creates no obligation on me to believe it, and this remains so even if I can not show that it's false (see Appeal to Ignorance), On the other hand, your obligation is only to defend it, not necessarily to convince me that it's true (good thing, since I may be an utter blockhead.) 

*Causal Reasoning C&P page: 242

Definition: Inference from premises concerning correlations, concurrence, covariance and other empirically observed connections, to conclusions about cause-and-effect relationships

Comment: Note that not every piece of reasoning about causation meets the terms of this definition. Consult our treatment of the Standard Pattern for Causal Arguments for more details about good causal reasoning.

4352 Geezengolian warriors threw up after attending the royal banquet. Queen Ho-Qwee-Zeen's legendary lizard-in-a-laprobe dinner must have made them sick! (Note: this is an example of causal reasoning, but not of good causal reasoning.) 

*Charitable Interpretation, Principle of: C&P page: 22

Definition: A rule for extracting arguments from unstructured or poorly- structured collections of statements, enjoining the extractor to construct from them the best possible argument, given the author's point of view.

Comment: In particular, it advises you to designate statements as premises and conclusion in such a way as to yield a valid argument, if possible, or one which can be made valid by addition of the smallest number of least- controversial premises. In other words, help the authors give you their best shot. Don't compliment yourself too much for charity, though-- the real reason for this careful reconstruction is that once the argument has been critiqued, it can't pop right back up with a few minor changes. 

*Composition, fallacy of: C&P page:

Definition: An argument which requires, but does not defend, the premise that if all the parts of a whole (or members of a set) have some quality Q, then the whole (or set) will also have quality Q.

Comment: Usually this premise will be implicit, but even when it is made explicit it will require further defense in any specific instance, since across the board it simply is not true.

"They've got Amos McFnerk, the world's greatest center. Two fantastic (great) forwards, and two awesome (great) guards. (Therefore) it's got to be a helluva (great) team!"

Sorry-- faulty argument! It's not true in general that what characterizes the parts will characterize the whole, and when it comes to athletic teams, it is notoriously false. A bunch of great players may be a bunch of prima- donnas and incapable of cooperation when combined into an "all-star" team. 

*Conceptual Theory C&P page: 202

Definition: A statement of the conditions under which a certain concept applies to an object. 

*conclusion C&P page: 16,43

Definition: In the technical sense, which refers to arguments and their structure, the conclusion is a statement which is supposedly given support by a set of other statements (the premises).

Comment: In real life, arguments frequently have several levels of sub- arguments-- that is, the overall conclusion will be supported by its set of premises, but any one of those premises may itself be supported by another set of statements, and so forth. Relative to the statement it supports, a statement is a premise; relative to those which it is supported by, it is a conclusion.

Note that its being a conclusion says nothing about where a statement will occur in a given presentation-tion. The conclusion could come first, last, or in the middle-- or, for that matter, it could be repeated several times throughout the presentation. And by no means is the last sentence in the presentation necessarily its conclusion. When a speaker says, "And in conclusion, I want to thank you for being such a wonderful audience. I'm outa here." -- that's not part of his argument at all. 

*conclusion, missing C&P page:

Definition: A statement which represents the conclusion the peddler apparently hopes the consumer will infer from the statements he presents, although it is not explicitly stated. 

*Conditional Statement a.k.a.: Hypothetical C&P page: 29

Definition: A statement of the "if-then" form, represented by A _> B in formal language. The "if" part is called the antecedent and the "then" part is called the consequent. 

*Conditioning the marketplace: C&P page:

Definition: One of any number of elements (verbal or not) which may function, in the propositional marketplace, to suppress a critical attitude among the consumers of a peddler's statements.

Comment: The symbols of honor and respectability adorning the peddler, music pumping through the PA system, bevies of foxy babes smiling and cheering, and a squad of goons going around to rough up dissenters-- all these are marketplace conditioners. The best anti-conditioner is a good course in critical thinking, that helps the consumer notice and counteract the conditioning effect. 

*confidence strategy : C&P page:

Definition: The practice of presenting a statement with style, volume, exclamation points, or other indicators of its truth, importance, or certainty, by way of concealing its lack of substantiation.

Comment: Yelling is the most common confidence device. In more cultured circles, one simply attaches confidence phrases to one's statements-- for example, "Obviously," "As anyone can see,", "Of course," etc., etc. 

*Conjunction C&P page: 121

Definition: A statement of the "and" form that links two other statements. 

*connective C&P page:

Definition: One of any number of so-called "logical operators" which make more complex statements out of simpler ones-- for example, "and", "or", "not", etc. 

*consequent C&P page: 27

Definition: (see conditional statementabove)

*Consistent C&P page: 109

Definition: A group of statements is consistent if it is logically possible for all of them to be true at the same time. 

*Consumers of Propositions

Definition: Those in a context of persuasion whose acceptance of certain statements is sought by the peddler of propositions. 

*Contradiction, Self- a.k.a.: Logical Absurdity C&P page: 388

Definition: A statement that cannot (logically) be true. 

*Controlled experiment C&P page: 247

Definition: An experiment designed to determine whether one thing causes another. It involves comparing an experimental group to which the suspected causal agent is applied, to a control group to which it is not, all other conditions being the same.

Comment: Doesn't avoid bias or reversed order. Does it avoid 3rd factors? Intervening intelligence? 

*Correlation, (Positive)C&P page: 242

Definition: Event Type A is positively correlated with Event Type B, if the percentage of As which are Bs is higher than the percentage of As which are not Bs. 

*counter-instance C&P page: 209

Definition: An example which demonstrates that a given generalization is not universally true.

Comment: Just to keep the lines of distinction clear, we use the term counter-instance in the context of establishing the truth-value of statements (Evaluation), and the term counter-example in the context of establishing the (in)validity of arguments (Assessment).

Tiger Woods constitutes a counter-instance to the generalization that all professional golfers are Caucasian. 

*Counterexample (to a pattern) C&P page: 90

Definition: A counterexample to an argument pattern consists of a real-life argument which matches that pattern and yet has 100% true premises and a false conclusion.

Comment: Obviously, such a counterexample demonstrates that the pattern in question is not valid-- i.e. can not be relied upon to generate valid arguments.

"A) If John Lennon was trampled by a herd of elephants, he died.
B) John Lennon was not trampled by a herd of elephants.
Therefore © John Lennon did not die."

This constitutes a counterexample to the (Jabberwock) argument pattern
"If A then B.
Not A.
Therefore not B." 

*Counterexample (to an argument) a.k.a.: Counter argumentC&P page: 261

Definition: A counter-example to an argument (as opposed to one to an argument pattern) constitutes (broadly) a demonstration that the premises of that argument could be true under certain conditions where the conclusion would nevertheless be false.

Comment: This demonstration will usually consist of adding a premise to the argument, that details a particular way in which the original premises could count as true, and under which it is at least not certain that the conclusion is true.

"Little Freddie had turned a blotchy yellow-green by now, and was running a temperature of 107. A scratchy ak-ak-ak escaped from his dry and wrinkled throat." You might be tempted to draw from these premises the conclusion that Little Freddie is sick (to say the least!). But now add in the premise that Freddie is a Geezengolian from the planet Zenith. Are you so sure now what's sick and what's normal? 

*Critical Reasoning a.k.a.: Critical Thinking C&P page:

Definition: In contrast to mere disagreement, a procedure for understanding and evaluating the given support for a point of view.

Comment: Specifically, this encompasses the various activities of Reconstruction, Assessment, and Evaluation-- that is, discerning what the argument is, determining its status as deductive/inductive/irrational, and judging the impeach able/impeccable status of its various premises. 

*Deductive Argument C&P page: 224

Definition: An argument in which the truth of the premises guarantees the truth of the conclusion, in the sense that there is no possible way for the premises all to be true when the conclusion is false.

Comment: We use the term deductive, in other words, as a synonym for valid. Not every argument presented as a deductive one (for example, by saying that in view of its premises its conclusion must be true) is really a deductive one (cf. the pseudo-inductive fallacy). 

*Denying the Antecedenta.k.a.: Jabberwock C&P page: 28

Definition: Any argument that exhibits the following invalid pattern: 1) If A then B. 2) Not A. Therefore, Not B.

Comment: We call it Jabberwock in honor of the prolific imagination of the 19th century mathematician and logician Charles Dodgson, better known as Lewis Carroll, author of Alice in Wonderland, Through the Looking Glass and dozens of other whimsical poems and tales, notably Jabberwocky, in which there occurs the dire warning to "Beware the Jabberwock, and shun the frumious Bandersnatch."

*Denying the Consequenta.k.a.: Modus Tollens C&P page: 28

Definition: A common, valid argument form in which the consequent of a conditional premise is "denied" by a second premise, which unconditionally negates that consequent term, thus following the pattern 1)If A, then B. 2) Not B. Therefore, Not A. 

*Disagreement C&P page: 3-4

Definition: Mere disagreement takes place when people assert opposing points of view without being open to having their minds changed by reasons. Each seeks to maintain a prior set of beliefs. 

*Disjunction, inclusivea.k.a.: and/or, inclusive or C&P page: 121

Definition: A connective yielding a complex "output" statement based on two simpler "input" statements, in such a way that the complex is True whenever either input statement is True, and false only when both inputs are false.

Comment: The word "or", in English, is ambiguous, since it can be taken as representing either inclusive-or or exclusive-or. The hybrid term "and/or", however, unambiguously represents the inclusive-or function. 

*Division, fallacy of C&P page:

Definition: An argument which requires, but does not defend, the premise that what applies to the whole (or group) will apply to all (or most) of the parts (or members).

Comment: This premise is not true in general, and therefore ought not be accepted as true without further defense in any specific topic area. The average number of children per family may be 2.2, but I dare say no one family has 2.2 children! 

*domino argument C&P page:

Definition: An argument characterized by a long chain of cause-to-effect inferences, leading from an apparently innocuous first step to a glaringly undesirable last one-- the upshot being that one should avoid the first step if at all possible.

Comment: Domino arguments are not necessarily either invalid or unsound. They're a great place to lose your critical cool, though-- as the peddler terrorizes you with the prospect of that last horrible step, you may overlook the many missing premises (of the "A causes B" format), and consequently fail to notice how many are seriously impeach able (typically, in need of further defense). 

*elementary logical questions C&P page:

Definition: A set of questions which, when combined with the disposition to ask them, characterize the attitude of a critical thinker.

Comment: These include: What does this say? What does this mean? What makes you think so? So what-- i.e., What follows from that? Why is that a reason? Does this follow from that? 

*equivalence C&P page:

Definition: Two statements are equivalent if and only if neither has truth- value T when the other has truth-value F.

Comment: Alternatively, we could say that two statements are equivalent if each follows from the other. Two statements which are equivalent by one definition will also be equivalent by the other. 

*Fallacy : C&P page: 150

Definition: A Fallacy is a pattern of reasoning which should not be persuasive (but frequently is).

Comment: The point of identifying something as a fallacy is to warn consumers away from it, because it can lead you to think you're being rational when you're not. Not every pattern of bad reasoning gets on the fallacy list-- nobody is tempted to think "This is blue. Therefore it's not blue." Not every instance of irrational persuasion involves a fallacy, either. If I browbeat you all to hell and gone, you may eventually believe just anything I say. I used no arguments, though, and thus no fallacies. 

*False dilemma a.k.a.: False Dichotomy C&P page: 153

Definition: 1) A disjunctive statement which is not a tautology. 2) An argument which requires such a statement as a premise, but does not defend it.

Comment: Typically, the premise (cf. definition 2) is not stated explicitly, which makes it harder for the consumer to realize it is in need of further defense. For example, an appeal to ignorance involves the false dilemma "It's known to be false (which you can't prove), or it's known to be true." Once the premise is brought to explicit attention, you see there a third possibility-- "it's not known either way".

"This isn't art-- it's vandalism!" Given the context of spray-painted graffiti on subway cars, we may assume that the presenter intended the judgment about art (an obscure subject) to be strengthened by the judgment about vandalism (plain to almost anyone). If so, there's a missing premise, namely "Either it's art or it's vandalism, but not both." This disjunctive statement may be true, but it isn't automatically true like "Either it's art, or it's not art" would be. 

*Follows : C&P page: 182

Definition: To say that statement P "follows" from a set of statements {S } is to say that an argument having the statements of S as premises and P as conclusion is a valid one.

Comment: If that argument is not valid, P doesn't follow from {S}, and the argument (or its conclusion) is called a non sequitur (which, in Latin means "It doesn't follow." ) 

*General-to-particular Reasoning : C&P page: 226

Definition: Nondeductive reasoning that moves from "statistical premises, including those using words like most, to a conclusion about a particular item. 

*Hasty Generalization : C&P page: 238

Definition: Embracing a generalization on the basis of a sample that is either too small or selected in a potentially biasing way. 

*hedgehog strategy : C&P page:

Definition: A practical strategy, based on the "one big secret" (the principle of burden of proof), designed to make domestic squabbles and common disputes into more constructive encounters. 

*holy cows : C&P page:

Definition: Any concept that, in a given cultural context, tends to be regarded automatically as good and thus remains immune to criticism.

Comment: They also tend to remain uncritiqued and undefended, which makes them a liability to their worshipers. For instance, having never been challenged to defend the value of democracy, a dyed-in-the-wool democrat is liable to being blind-sided by an articulate aristocrat. 

*Impeach able Premises : C&P page:

Definition: A premise is said to be impeach able if a) it is false, or b) it is in need of further defense before it can be accepted as true, or c) its meaning is sufficiently indeterminate (i.e. too vague, or crucially ambiguous) that its truth value can also not be unambiguously determined.

Comment: Premises that are not impeach able are referred to as impeccable. 

*Implicit Premise : C&P page: 45

Definition: A carefully selected statement that, when added to the premises of an invalid argument, converts it into a valid one.

Comment: Among the criteria of careful selection are that the statement must not contradict itself, nor any explicitly stated premise, nor the peddler's general viewpoint; it should make maximal logical use of the explicit premises; and, within those limits, it should be as general as plausibility of its truth will permit. 

*in foro interno : C&P page:

Definition: "In the internal forum", i.e. in the mind of the critical thinker, who reflexively questions her own thought processes as much as she does those of a peddler in an external propositional marketplace. 

*Inductive Argument : C&P page:

Definition: An argument in which the premises do not guarantee the conclusion, but do cast a high (>50%) probability on it.

Comment: When the premises of an inductive argument are true, and there is no defeating evidence, the conclusion is given a high (>50%) probability of truth.

"Most elves are green. Olaf is an elf. So Olaf is green." Obviously it doesn't follow from these premises that Olaf is green, but, in view of the premises, "Olaf is green" is more probable than "Olaf is not green." If you know only that the premises are true, you still don't know that Olaf is green, but other things being equal, that's your best guess. 

*inference indicator : C&P page: 17,2p

Definition: Any of a vast number of words or phrases commonly used to indicate that a statement is to be seen as part of an argument-- i.e., as a premise or conclusion.

Comment: Very few such phrases have only that function, so critical judgment is still required in Reconstruction, even if a presentation is crawling with inference indicators. "Thus", "therefore", "so", and "consequently" commonly indicate that an upcoming statement is a conclusion relative to some previous statements. "Since,""After all," and "In view of the fact that" commonly indicate that an upcoming statement is a premise. 

*ipsedixitism : C&P page:

Definition: An statement asserted but not defended.

Comment: The term is derived from the Latin words "dixit" (he says) and "ipse" (himself), and was coined by the British philosopher Jeremy Bentham. 

*irrational argument : C&P page:

Definition: An argument which is neither deductive (valid) nor inductive; thus, one whose premises do not make its conclusion any more probable than not. 

*Logic C&P page:

Definition: The study of the principles of rational inference. 

*logical possibility C&P page: 89

Definition: A statement which is not self-contradictory. Relative to a given consistent set of statements, a statement is a logical possibility if in adding it to the set consistency is preserved. 

*Negation C&P page: 121

Definition: a) A logical operation which, from a given "input" statement, yields another statement which has truth-values precisely the opposite of those of the original. b) the output statement produced by such an operation.

Comment: The negation function is performed in English in a variety of ways, inserting the word "not" at the grammatically appropriate point being the most common. Thus "The moon is not blue," represents the negation of the statement "The moon is blue." Precatory phrases such as "It is false that..." or "It is not the case that..." or "You would be mistaken to believe that ..." also serve the negation function. 

*Nondeductive Argument : C&P page: 224

Definition: An argument in which the premises are not put forward to logically guarantee the truth of the premises. 

*Particular-to-General Reasoning : C&P page: 225ff

Definition: A type of nondeductive argument that typically moves from evidence about particulars (for example, evidence collected through sampling) to conclusions about a larger population. 

*Peddler of Propositions: C&P page:

Definition: One who makes assertions, in the propositional marketplace, with the intention obtaining agreement with them from a target audience (the propositional consumers).

Comment: In normal circumstances, individuals switch smoothly back and forth between the peddler and consumer roles, even relative to a given statement-- and certainly relative to different statements. No one is permanently and solely a peddler, and few if any are solely consumers. 

*Persuasion, Context ofPropositional Marketplace C&P page:

Definition: Circumstances in which one or more persons (the propositional peddlers) assert statements with the objective of getting one or more other persons (the consumers) to accept these statements as true.

Comment: (Alternate) A statement is made in a context of persuasion if it is asserted, or offered as true, with the intention of getting someone to believe it. 

*process of eliminationa.k.a.: disjunctive syllogism C&P page:

Definition: A valid argument pattern consisting of premises
1) P or Q
2) not-P with
conclusion Q. 

*process of specification: C&P page:

Definition: A valid argument pattern consisting of premises
1) P or Q
2) P with
conclusion not-Q.

Comment: The or here represents exclusive-or (see entry for same), as opposed to and/or. 

*question, rhetorical : C&P page:

Definition: A phenomenon in English usage wherein a sentence having the form of a question functions to express a statement.

Comment: There's also the phenomenon of the rhetorical exclamation (and many other ways of expressing statements without using declarative sentences). It's up to the astute reconstructer to figure out what a person is trying to say with these various verbal devices.


Joe: Would you like a beer?

Bob (by way of reply): Is the Pope Catholic? Does a bear growl in the woods?

*reconstruction : C&P page: 18,42

Definition: The process of developing a structured argument from a collection of sentences issued by the peddler in a propositional marketplace. 

*reductio ad absurdum a.k.a.: Reduce to the Absurd C&P page: 149

Definition: A method of establishing the validity of an argument by showing

that its premises are not logically consistent with a rejection (negation) of

its conclusion.

Comment: Or, in other words, accepting the premises contradicts rejecting the conclusion. The way reductio shows this is by combining the premises with the negation of the conclusion, and showing that this leads to a self- contradiction. 

*selection of evidence : C&P page:

Definition: An extra-logical marketplace device (like lying and evasion) wherein a peddler offers only the facts that tend to support the proposition being peddled, and ignores or suppresses those which would tend to weigh against it.

Comment: Since the object of a critical thinking course is to enable a person to live a rational and reasonably well-informed life without necessarily being an expert in all fields (or having a head full of trivia), we have developed the concept of potential selection of evidence as a guide to asking questions of the experts. 

*Slippery Slope Argument: C&P page: 154

Definition: An argument that requires, but does not defend, the premise that to accept a specific course of action would be to embrace a general principle that would apply equally well to other, plainly undesirable sorts of action. It concludes that the proposed action should be rejected.

Comment: While superficially similar to the domino argument, in slippery slope the connection between the proposed specific action and the clearly undesirable one is supposed to be a logical one, while in the domino argument it is alleged to be one of cause-and-effect.

You heard this sort of thing from your third grade teacher, who said she couldn't let you bring your pet turtle to school because if she did, then to be consistent she'd have to let every other kid bring his pet to school, and who knows, somebody might have an elephant! 

*Sound Argument : C&P page: 86,104, 151

Definition: A valid (deductive) argument with only true premises. 

*Strawman : C&P page: 155

Definition: Broadly, dismissing a position by substituting another in place of it and directing one's critique toward this substitute instead.

Comment: Naturally this is effective only if the substitute looks enough like the original to fool the right observers. Users of the strawman strategy sometimes fool even themselves, since they are more often careless than they are dishonest. The examples in Cedarblom and Paulsen exemplify this idea to a degree, but mix into the picture certain other fallacies which deserve independent analysis. See false dilemma, and critique. 

*syllogism : C&P page: 29,89

Definition: In the classic sense, a syllogism is an argument composed of three statements each of which connects any two of the same set of three categories and is of the form All X are Y, No X are Y, Some X are Y, or Some X are not Y.

Comment: In the example below, the three categories are "students" (A), "smart people" (B), and "rich people" (C). The three statements involved thus reflect the patterns Some A are B, No B are C, and Some A are not C, respectively.

"Some students are smart people. No smart people are rich people. Therefore, some students are not rich people."


*tautology : C&P page:

Definition: Broadly speaking, a tautology is any statement whose truth- value is True regardless of the truth-value any other statements may happen to have-- in other words, it's true in all possible situations.

There are no mountains over 15,000 feet high, or there is at least one such mountain. 

*terminological obfuscation: C&P page:

Definition: The practice of disguising simple notions in complicated terminology, in order to conceal the true significance (or lack thereof) from the ordinary propositional consumer.

Comment: A chemist might refer to what's in the shaker on your table as "sodium chloride", or "NaCl". You may be baffled by these terms, but in fact they function to increase clarity and precision. On the other hand, when the CIA takes somebody out and shoots him, they may speak of it as "termination with extreme prejudice", but here the phrase hides the reality rather than revealing it details.

Instead of "terminological obfuscation" we could simply have said "clouding things up with words", but if we had, you might get the idea that logic teachers don't really know anything very special. 

*Truth-Value : C&P page: 131

Definition: One of two possible statuses a statement may have, namely "true" or "false".

Comment: Never mind how a statement gets its truth-value, but it's got the one it's got, whether you know it or not. The best humans can hope for, in this context, is to discover what truth-value a statement has. A person who knows the truth-value of lots of statements is said to be well-informed. 

*tu quoque a.k.a.: "You Too" C&P page: 182

Definition: A strategy which aims to discredit a peddler's statement (typically when it is a recommendation or evaluation) on the grounds that the peddler's own life or actions are inconsistent with view the peddler is promoting.

Comment: Tu quoque is a type of ad hominem, since it attempts to evaluate a person's views by evaluating the person. It would be nice if everyone could and would walk it like they talk it, but the fact they can't or won't doesn't necessarily mean their views have no merit.


Father: No, you should not smoke. It's habit-forming, and it'll ruin your health!

Daughter: Ha! Look who's talking- Mr. 2-Packs-a-Day himself! Get your act together, Pops, and then maybe you can expect me to listen to your commandments! 

*Validity : C&P page: 30,86,131,146

Definition: An argument is valid (deductive) if and only if there are no possible circumstances under which all the premises would be true, and the conclusion would be false. 

*weasel word : C&P page:

Definition: A innocuous-looking word or phrase which accompanies an otherwise dramatic or mind-catching assertion, serving to reduce its risk of being false while not distracting from its powerful impact.

Comment: This definition was constructed by Lauren Miller, a man who is possibly one of the most brilliant and creative individuals whose work you'll ever have the privilege of reading... well, maybe not very possibly-- it may depend on whether your reading goes beyond the blurbs on your breakfast cereal box.

Last Modified: 9/30/11