A few months ago we did a theme on Terms of Logic. As a natural counterpart, let's look at terms of illogic.

amphibology; amphiboly – an ambiguity which results from ambiguous grammar

An amphibology is often so obvious that it humorous rather than misleading. "One morning I shot an elephant in my pajamas. How he got into my pajamas I'll never know." – Groucho Marx, in the movie Animal Crackers)

But the ambiguity can mislead the hearer to an illogical conclusion. When King Croesus consulted the Oracle at Delphi about his military plans, the response was, "If Croesus crosses the Halys, a great power will be destroyed." Croesus took this as predicting victory for him. In the fact, when he crossed the River Halys into Persia, a great army was indeed destroyed; but unhappily for him, the army annihilated was his own.

The oracle gave us our bonus word:
delphic – obscurely prophetic; also, ambiguous; mysterious

Thanks, wordcrafter, for triggering an old memory. Two words came to mind when I saw amphiboly. ("Amphi" related to "ambi" or two, and "boly," or thrown.)

The first is "zeugma" meaning yoked together -- use of a word to govern two or more words though appropriate to only one; "`Mr. Pickwick took his hat and his leave.'

The second is "syllepsis" --use of a word to govern two or more words though agreeing in number or case etc. with only one.
(both www.cogsci.princeton.edu/cgi-bin/webwn)
It seems the first is more a logic error, while the second relates to grammatical ambiguity.

I enjoy "nice" distinctions -- chaconne vs. passagaglia, hurling vs. shinty, even the original vs. current meanings of "nice."

A post on our board has asked, "Is amphibology [yesterday's word] usually an ambiguous statement because of grammar...or could it just be an ambigous statement?"

Technically, amphibology is an abiguity of grammar. In contrast,

equivocation – the type of ambiguity which occurs when a single word or phrase is ambiguous; this this ambiguity is not grammatical but lexical. [Obviously, 'equivocation' has other and more familiar meanings.]

Equivocation, like amphibology, can often be humorous, as in the Who's on First comedy routine (text or hilarious audio), and it is often the basis of humorous headlines. Among the bloopers in Headlines That You Just Have to Hang On To, by Bob Levy of the Washington Post, you'll find such examples as

Panda Mating Fails; Veterinarian Takes Over."
"Key Witness Takes Fifth in Liquor Probe."
"Marijuana Issue Sent to Joint Committee."

But equivocation, like amphibology, can also mislead the hearer.

... humanity has a right not to be killed, at least. Without laying out all the evidence here, it is fair to conclude from medicine that the humanity of the life growing in a mother's womb is undeniable and, in itself, a powerful reason for treating the unborn with respect.
– Helen M. Alvaré, The Abortion Controversy (Greenhaven, 1995)

The equivocation lies between two meanings of "human": 1. a person as a whole ("human being"), which has a right not to be killed, and 2. a part of a person ("the human hand"), which though undeniably human has no such right. Alvaré is confuting the two senses. Her fallacy would be would be obvious if the passage read, "Humanity has a right not to be killed, and the humanity of the human hand is undeniable." Of course, Alvaré makes perfect sense if you assume that a fetus is a human being, but that would almost be assuming the desired conclusion.

[I thank The Fallacy Files for much of the matter in the last two days, and expect to use it further this week.]

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argument ad hominem – countering an opponent's argument by attacking the opponent, rather than the argument he makes.
[In effect, an attempt to change the subject from the matter at hand, and focus instead on the opponent personally. This is a failure of logic, in that the validity of an argument does not depend on the person making it.]

An ad hominem argument may be either 'abusive' or 'circumstantial':

• abusive ad hominem – attacking the opponent's character or other personal qualities:
  "I once asked a long-haired maggot-infested FM-type environmentalist wacko who he thought was threatening the owl." – Rush Limbaugh, The Way Things Ought to Be
• circumstantial ad hominem – attacking the opponent's personal circumstances:
  "When Attorney General Lisa Madigan gave a legal opinion that the proposal would be unconstitutional, the Governor remarked that she did so because of her father's (the Speaker of the Illinois House, Michael Madigan) influence. [Governor] Blagojevich's comment was an unfair, ad hominem attack." – The Illinois Leader, June 08, 2004

Apparently John Locke coined the term 'ad hominem' (An Essay Concerning Human Understanding, 1690), and Schopenhauer was the first to distinguish the abusive fallacy from other forms (The Art of Controversy).

Some dictionaries have definitions which I suggest are incorrect:

• M-W online: 1. appealing to feelings or prejudices rather than intellect.
  [But "appeal to emotion" is a separate fallacy, and it need not be directed at the opponent personally. Conversely, an ad hominem argument focuses on the opponent but need not play upon emotions, although it of course often does so.]
• same: 2. marked by an attack on an opponent's character.
  [But only the abusive form of 'ad hominem' deals with 'character'.]
  
• AHD: appealing to personal considerations rather than to logic or reason.
  [That definition encompasses an appeal to interest, such as, "Support me, because I'll pay you for it." But the 'personal consideration' in an ad hominem are those of about opposing opponent, not those about the audience.]

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tu quoque [Latin for "you too," or more loosely, "So's your old man."] – a retort charging an adversary with being or doing what he criticizes in others
. . .In ad hominem argument the accused hurls a charge against his accuser. Tu quoque is a type of ad hominem, in which he hurls back the very charge of which he stands accused. Logically, this is irrelevant to whether the accused is himself guilty. But tu quoque can be very effective, by putting the accuser on the defensive.

. . ."I say, what HAS happened since I saw you last, Sally?" Philip began.
. . ."Nothing that I know of."
. . ."I believe you've been putting on weight."
. . ."I'm sure you haven't," she retorted. "You're a perfect skeleton."
. . .Philip reddened.
. . ."That's a tu quoque, Sally," cried her father. "You will be fined one golden hair of your head. Jane, fetch the shears."
. . ."Well, he is thin, father," remonstrated Sally. "He's just skin and bone."
. . ."That's not the question, child. He is at perfect liberty to be thin, but your obesity is contrary to decorum."
– W. Somerset Maugham, Of Human Bondage,, ch. CI

The following is from a 1997 CNN interview with Osama Bin Laden, about 40% of the way down in the full interview. Nowhere in Bin Ladin's long answer (here given in full) does he ever addresses the question posed ("Do you sponsor terrorism?"); he simply makes that very same accusation against the US.

REPORTER: Now, the United States government says that you are still funding military training camps here in Afganistan for militant, Islamic fighters and that you are a sponsor of international terrorism; but others describe you as the new hero of the Arab-Islamic world. Are these accusations true? How do you describe yourself?

BIN LADIN: After the collapse of the Soviet Union in which the U.S. has no mentionable role, but rather the credit goes to God, Praise and Glory be to Him, and the Mujahidin in Afghanistan, this collapse made the US more haughty and arrogant and it has started to look at itself as a Master of this world and established what it calls the new world order. It wanted to delude people that it can do whatever it wants, but it can't do this. It leveled against me and others as many accusations as it desired and wished. It is these (accusations) that you mentioned. The US today as a result of the arrogant atmosphere has set a double standard, calling whoever goes against its injustice a terrorist. It wants to occupy our countries, steal our resources, impose on us agents to rule us based not on what God has revealed and wants us to agree on all these. If we refuse to do so, it will say you are terrorists. With a simple look at the US behaviors, we find that it judges the behavior of the poor Palestinian children whose country was occupied: if they throw stones against the Israeli occupation, it says they are terrorists whereas when the Israeli pilots bombed the United Nations building in Qana, Lebanon while was full of children and women, the US stopped any plan to condemn Israel. At the time that they condemn any Muslim who calls for his right, they receive the highest top official of the Irish Republican Army (Gerry Adams) at the White House as a political leader, while woe, all woe is the Muslims if they cry out for their rights. Wherever we look, we find the US as the leader of terrorism and crime in the world. The US does not consider it a terrorist act to throw atomic bombs at nations thousands of miles away, when it would not be possible for those bombs to hit military troops only. These bombs were rather thrown at entire nations, including women, children and elderly people and up to this day the traces of those bombs remain in Japan. The US does not consider it terrorism when hundreds of thousands of our sons and brothers in Iraq died for lack of food or medicine. So, there is no base for what the US says and this saying does not affect us, because we, by the grace of God, are dependent on Him, Praise and Glory be to Him, getting help from Him against the US. As for the last part of your question, we are fulfilling a duty which God, Praise and Glory be to Him, decreed for us. We look upon those heroes, those men who undertook to kill the American occupiers in Riyadh and Khobar (Dhahran). We describe those as heroes and describe them as men. They have pulled down the disgrace and submissiveness off the forehead of their nation. We ask Allah, Praise and Glory be to Him, to accept them as martyrs.

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ipse dixit [typical use] – an unsupported dogmatic assertion
ipse dixit [broader usage] – argument from supposedly conclusive authority, rather than from reasoned evidence.
Also called appeal to authority or argumentum ad verecundiam.. May be used to prove [As in the old medieval view "Aristotle says" was conclusive proof] or to refute ["Eugenics? The Nazis were the first to practice eugenics."].

The broader concept is familiar to anyone who has heard a teenager say, "Janet's parents let her go to R-rated movies. Tim's parents let him go to R-rated movies; even Margaret is allowed to go to R-rated movies, and you know how strict her parents are! Why can't I go?" (Henriette A. Klauser, Writing on Both Sides of the Brain)

For the more typical usage, here are a recent example and an older one.

Judge have no special competence, qualifications, or mandate to decide between equally compelling moral claims (as in the abortion controversy) or equally compelling political clams (counting ballots by hand or stopping the recount because the standard is ambiguous. ... these are precisely the sorts of issues that should be left to the rough-and-tumble of politics rather than the ipse dixit of five justices.
– Alan M. Dershowitz, Supreme Injustice: How the High Court Hijacked Election 2000

Judge Douglas recurs again, as he did upon one or two other occasions, to the enormity of Lincoln – insignificant individual like Lincoln – upon his ipse dixit charging a conspiracy upon a large number of members of Congress, the Supreme Court and two Presidents, to nationalize slavery. I want to say that, in the first place, I have made no charge of this sort upon my ipse dixit. I have only arrayed the evidence tending to prove it, and presented it to the understanding of others, saying what I think it proves, but giving you the means of judging whether it proves it or not. This is precisely what I have done. I have not placed it upon my ipse dixit at all.
– Abraham Lincoln, in his debates with Steven Douglas (Second Debate, Freeport, Illinois), August 27 (28?), 1858

post hoc – the logical fallacy of concluding that if one thing happens after another, the first must is the cause of the second.
[Short for Latin post hoc, ergo propter hoc "After this, therefore because of this." The term is also used where one draws such a conclusion when two events coincide]

If A and B occur together, A might cause B. But perhaps B causes A; or they have a separate common cause; or they coincide by mere coincidence.

It is easy to find comic examples ("Wind is caused by the trees waving violently, stirring up the air"), but let's start with a serious one.

. . .What might happen if an entire nation got a flu vaccine? By chance alone, tens of thousands of people would come down with some illness and some would die. After all, tens of thousands of people get sick and many die every day. But what would a jury say if confronted with a child who began having severe epileptic seizures within hours of being immunized against swine flu? How sympathetic might a jury be to a large company that argued that the epilepsy was coincidental when they saw the tearful parents?
. . .It was simply not worth taking the chance, the [vaccine] companies reasoned. [An independent authority's letter to the New York Times] explained that if Americans have flu shots in the numbers predicted, many as 2,300 will have strokes and 7,000 will have hearts attacks within two days of being immunized. "Why? Because that is the number statistically expected, flu shots or no flu shots," he wrote. "Yet can one expect a person who received a flu shot at noon and who that same night had a stroke not to associate somehow the two in his mind? Post hoc, ergo propter hoc. It is one thing to see matters objectively in light of statistical expectations. It is quite another when it affects one personally. Who can blame someone for assuming the events are linked." Gina Bari Kolata, Flu: The Story of the Great Influenza Pandemic of 1918 (Ch. 6: A Litigation Nightmare) quote simplified for brevity

post hoc, ergo propter hoc – Latin for "It happened after, so it was caused by" (e.g., Jaime Cardinal Sit, Archbishop of Manila: "I know of … a 26-year old who looks 60 because she takes [contraceptive] pills."
– Carl Sagan, The Demon-Haunted World: Science As a Candle in the Dark (Ch 12: The Fine Art of Baloney Detection)

"Near-perfect correlations exist between the death rate in Hyderabad, India, from 1911 to 1919, and variations in the membership of the International Association of Machinists during the same period. Nobody seriously believes that there is anything more than a coincidence in that odd and insignificant fact."
David Hackett Fischer, Historians' Fallacies: Toward a Logic of Historical Thought (as quoted in Fallacy Files)

false dilemma – two alternatives set up as if they were the only options, when there are in fact middle-ground or other options. [also known as bifurcation, black-and-white fallacy, either/or fallacy] Pithy sloganeering often uses the false dilemma (e.g., "America: Love it or leave it"), ignoring possible middle grounds.

It's useful to contrast contrary with contradictory. If I say, "It's hot today," you contradict me if you simply deny, and say, "It's not hot" (one or the other of us is right). But to assert the contrary is to take the opposite position, "It's cold" (we each may be wrong). The "love it or leave it" slogan treats two contrary alternatives as if they were contradictory, with no other choice.

[Several] e-mail messages from readers asked: "Would you rather fight them over there or over here?" Whether they knew it or not, these readers were setting up what is known as a "false dilemma," providing a limited number of options (usually two), when there are actually more than that, in this case dozens, perhaps hundreds more. Another famous example of a false dilemma is President Bush's statement "You're either with us or with the terrorists." Again, many more possibilities exist here than the "either/or" option put forward by Bush.
– Bruce Mulkey, Asheville (North Carolina) Citizen-Times, June 11, 2004, whose very headline critiques a false dilemma, saying, "There is absolutely nothing patriotic about meekly going along with anything our president wants."

Wordcrafter notes:
- I'm not suggesting that "false dilemmas" come only or principally from only one side of the political aisle.
- Here is the full context of Bush's remark, beyond what Mulkey quotes: "Every nation, in every region, now has a decision to make. Either you are with us, or you are with the terrorists. From this day forward, any nation that continues to harbor or support terrorism will be regarded by the United States as a hostile regime."

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A half-decade of mounting political scandals have [sic] turned Connecticut into a punchline of political backwardness. ... said Gian-Carlo Peressutti, ... "It begs the question of why does a state that has so much wealth and intelligence and talent continue to produce public servants who continue to let those that they serve down. I think that's a fair question."
– Avi Salzman, The New York Times, June 27, 2004

Peressutti uses "beg the question" to mean "raises or leads inevitably to the question". That's the common usage but not the original meaning, and the authorities disagree over whether that newer usage is proper. The original meaning referred to a certain logical fallacy.

begging the question – argument by taking for granted, and uses as a premise, the very conclusion to be proved. [The Latin phrase is petitio principii, which I understand to mean 'pleading for the principle'. Can Latin scholars confirm or correct?] One web-author gives this example:

When a student accuses me of grading him unfairly because no matter how "excellent" his papers are, I never give them above a C, he is basing his argument that I grade unfairly on the unproven premise that his essays are excellent. (You'd be surprised at how often teachers hear just such arguments. On second thought, maybe you wouldn't be surprised at all.)

One can see how the phrases 'begging the question ' might be understood in the newer way. But why would the word 'begging' be used for this sort of logical fallacy? What do our readers think?

Michael Quinion's World Wide Words site has another of his excellent articles on this subject.