Newsgroup: italia.genova.discussioni
Titolo: 3a Repubblica?

La 2a Repubblica è implosa. Siamo davvero nella 3a Repubblica?
L'esito elettorale è chiaro. C'è cambiamento, governabilità, una
proposta vincente e legittimata, una opposizione omologata al sistema,
un quadro politico semplificato. Il nuovo assetto politico prospetta
un consolidamento duraturo.
Non siamo certo al 18 aprile 1948 (60 anni oggi!), ma quasi.
Come sempre, accetto l’esito elettorale con serenità e come base di
partenza per le riflessioni successive, mai per accusarmi di ciò che
ho fatto in buona fede o accusare altri, tantomeno gli elettori nel
suo complesso.
Questa volta, peraltro, mi resta il dubbio di aver assistito ad una
campagna elettorale virtuale.
Date voi già per scontato che il compromesso storico tra laici e
cattolici, tra comunisti, riformisti e moderati, tra capitale e
lavoro, tra liberismo, dirigismo e corporativismo sia già attuato?.
Date per scontato che la proposta elettorale del PD sia corrispondente
ai sentimenti della generalità dei cittadini che hanno votato per lo
stesso PD alle primarie e il 13 e 14 aprile?  Io no. E voi?
E date per scontato che si riscontrerà l’aggregazione necessaria per
governare tra i partiti del centro-destra? Io no. E voi?
Certo, ci sarà quella che deriva tra chiunque detenga il potere. Non è
scontata, per il resto, l’aggregazione tra partiti diversi legati solo
dal pensiero unico di un leader che non può mai aver torto, né
invecchiare.
Se il mio dubbio fosse proponibile, non inizierebbe ora la 3a
Repubblica, ma la 1a della nuova serie delle Repubbliche futuristiche,
quelle senza rivoluzioni, che implodono improvvisamente quando ce ne
informa la TV.
Su questo mio dubbio chiedo un franco parere anche qui, dove si va
anche a cercare il pelo nell’uovo.
18/04/08. Elio.

 Su questo mio dubbio chiedo un franco parere anche qui
A tua sorella l'hai già chiesto, vero?



Si', e mi ha detto di chiedere alla tua, che hai sempre fatto passare
per puttana (anche se poi corre voce che a far la vita travestito da
donna sei tu).
20/04/08. Elio.

Elio:
 X-Complaints-To: 
ab...@tiscali.it

 anche a cercare il pelo nell’uovo.
Chiedi al tuttologo.
Ti sapra' dare una risposta brillante.
-- 
Guardate quest'uomo: sembra deficiente e parla come un deficiente, ma 
non lasciatevi ingannare: è veramente deficiente!
Groucho Marx

 Boh, non so.
Che sia lui, o sia un geniale fake, è lui.
Purtroppo mi son "plonkato", e tanto non riesco a leggermi, che ero a
tutt'oggi convinto di non essere stato "clonato". 



FALLACIE E COSTRUZIONE LOGICA degli argomenti.
Introduction
There is a lot of debate on the net. Unfortunately, much of it is of
very low quality. The aim of this document is to explain the basics of
logical reasoning, and hopefully improve the overall quality of
debate.
The Concise Oxford English Dictionary defines logic as "the science of
reasoning, proof, thinking, or inference." Logic will let you analyze
an argument or a piece of reasoning, and work out whether it is likely
to be correct or not. You don't need to know logic to argue, of
course; but if you know even a little, you'll find it easier to spot
invalid arguments.
There are many kinds of logic, such as fuzzy logic and constructive
logic; they have different rules, and different strengths and
weaknesses. This document discusses simple Boolean logic, because it's
commonplace and relatively easy to understand. When people talk about
something being "logical," they usually mean the type of logic
described here.
What logic isn't
It's worth mentioning a couple of things which logic is not.
First, logical reasoning is not an absolute law which governs the
universe. Many times in the past, people have concluded that because
something is logically impossible (given the science of the day), it
must be impossible, period. It was also believed at one time that
Euclidean geometry was a universal law; it is, after all, logically
consistent. Again, we now know that the rules of Euclidean geometry
are not universal.
Second, logic is not a set of rules which govern human behavior.
Humans may have logically conflicting goals. For example:
John wishes to speak to whomever is in charge. 
The person in charge is Steve. 
Therefore John wishes to speak to Steve. 
Unfortunately, John may have a conflicting goal of avoiding Steve,
meaning that the reasoned answer may be inapplicable to real life.
This document only explains how to use logic; you must decide whether
logic is the right tool for the job. There are other ways to
communicate, discuss and debate.
Arguments
An argument is, to quote the Monty Python sketch, "a connected series
of statements to establish a definite proposition."
Many types of argument exist; we will discuss the deductive argument.
Deductive arguments are generally viewed as the most precise and the
most persuasive; they provide conclusive proof of their conclusion,
and are either valid or invalid.
Deductive arguments have three stages:
premises 
inference 
conclusion
However, before we can consider those stages in detail, we must
discuss the building blocks of a deductive argument: propositions.
Propositions
A proposition is a statement which is either true or false. The
proposition is the meaning of the statement, not the precise
arrangement of words used to convey that meaning.
For example, "There exists an even prime number greater than two" is a
proposition. (A false one, in this case.) "An even prime number
greater than two exists" is the same proposition, reworded.
Unfortunately, it's very easy to unintentionally change the meaning of
a statement by rephrasing it. It's generally safer to consider the
wording of a proposition as significant.
It's possible to use formal linguistics to analyze and rephrase a
statement without changing its meaning; but how to do so is outside
the scope of this document.
Premises
A deductive argument always requires a number of core assumptions.
These are called premises, and are the assumptions the argument is
built on; or to look at it another way, the reasons for accepting the
argument. Premises are only premises in the context of a particular
argument; they might be conclusions in other arguments, for example.
You should always state the premises of the argument explicitly; this
is the principle of audiatur et altera pars. Failing to state your
assumptions is often viewed as suspicious, and will likely reduce the
acceptance of your argument.
The premises of an argument are often introduced with words such as
"Assume," "Since," "Obviously," and "Because." It's a good idea to get
your opponent to agree with the premises of your argument before
proceeding any further.
The word "obviously" is also often viewed with suspicion. It
occasionally gets used to persuade people to accept false statements,
rather than admit that they don't understand why something is
"obvious." So don't be afraid to question statements which people tell
you are "obvious"--when you've heard the explanation you can always
say something like "You're right, now that I think about it that way,
it is obvious."
Inference
Once the premises have been agreed, the argument proceeds via a
step-by-step process called inference.
In inference, you start with one or more propositions which have been
accepted; you then use those propositions to arrive at a new
proposition. If the inference is valid, that proposition should also
be accepted. You can use the new proposition for inference later on.
So initially, you can only infer things from the premises of the
argument. But as the argument proceeds, the number of statements
available for inference increases.
There are various kinds of valid inference--and also some invalid
kinds, which we'll look at later on. Inference steps are often
identified by phrases like "therefore ..." or "... implies that ..."
Conclusion
Hopefully you will arrive at a proposition which is the conclusion of
the argument - the result you are trying to prove. The conclusion is
the result of the final step of inference. It's only a conclusion in
the context of a particular argument; it could be a premise or
assumption in another argument.
The conclusion is said to be affirmed on the basis of the premises,
and the inference from them. This is a subtle point which deserves
further explanation.
Implication in detail
Clearly you can build a valid argument from true premises, and arrive
at a true conclusion. You can also build a valid argument from false
premises, and arrive at a false conclusion.
The tricky part is that you can start with false premises, proceed via
valid inference, and reach a true conclusion. For example:
Premise: All fish live in the ocean 
Premise: Sea otters are fish 
Conclusion: Therefore sea otters live in the ocean 
There's one thing you can't do, though: start from true premises,
proceed via valid deductive inference, and reach a false conclusion.
We can summarize these results as a "truth table" for implication. The
symbol "=>" denotes implication; "A" is the premise, "B" the
conclusion.  
Truth Table for Implication 
Premise    Conclusion    Inference 
A                 B                      A => B 
false           false               true 
false           true                 true 
true            false                false 
true            true                  true 
If the premises are false and the inference valid, the conclusion can
be true or false. (Lines 1 and 2.) 
If the premises are true and the conclusion false, the inference must
be invalid. (Line 3.) 
If the premises are true and the inference valid, the conclusion must
be true. (Line 4.) 
So the fact that an argument is valid doesn't necessarily mean that
its conclusion holds - it may have started from false premises.
If an argument is valid, and in addition it started from true
premises, then it is called a sound argument. A sound argument must
arrive at a true conclusion.
Example argument
Here's an example of an argument which is valid, and which may or may
not be sound:
Premise:    Every event has a cause 
Premise:    The universe has a beginning 
Premise:    All beginnings involve an event 
Inference: This implies that the beginning of the universe involved an
event 
Inference:     Therefore the beginning of the universe had a cause 
Conclusion: The universe had a cause 
The proposition in line 4 is inferred from lines 2 and 3. Line 1 is
then used, with the proposition derived in line 4, to infer a new
proposition in line 5. The result of the inference in line 5 is then
restated (in slightly simplified form) as the conclusion.
Spotting arguments
Spotting an argument is harder than spotting premises or a conclusion.
Lots of people shower their writing with assertions, without ever
producing anything you might reasonably call an argument.
Sometimes arguments don't follow the pattern described above. For
example, people may state their conclusions first, and then justify
them afterwards. This is valid, but it can be a little confusing.
To make the situation worse, some statements look like arguments but
aren't. For example:
"If the Bible is accurate, Jesus must either have been insane, a liar,
or the Son of God."
That's not an argument; it's a conditional statement. It doesn't state
the premises necessary to support its conclusion, and even if you add
those assertions it suffers from a number of other flaws which are
described in more detail in the Atheist Arguments document.
An argument is also not the same as an explanation. Suppose that you
are trying to argue that Albert Einstein believed in God, and say:
"Einstein made his famous statement 'God does not play dice' because
of his belief in God."
That may look like a relevant argument, but it's not; it's an
explanation of Einstein's statement. To see this, remember that a
statement of the form "X because Y" can be rephrased as an equivalent
statement, of the form "Y therefore X." Doing so gives us:
"Einstein believed in God, therefore he made his famous statement 'God
does not play dice.'"
Now it's clear that the statement, which looked like an argument, is
actually assuming the result which it is supposed to be proving, in
order to explain the Einstein quote.
Furthermore, Einstein did not believe in a personal God concerned with
human affairs--again, see the Atheist Arguments document.
We've outlined the structure of a sound deductive argument, from
premises to conclusion. But ultimately, the conclusion of a valid
logical argument is only as compelling as the premises you started
from. Logic in itself doesn't solve the problem of verifying the basic
assertions which support arguments; for that, we need some other tool.
The dominant means of verifying basic assertions is scientific
enquiry. However, the philosophy of science and the scientific method
are huge topics which are quite beyond the scope of this document.
Fallacies
There are a number of common pitfalls to avoid when constructing a
deductive argument; they're known as fallacies. In everyday English,
we refer to many kinds of mistaken beliefs as fallacies; but in logic,
the term has a more specific meaning: a fallacy is a technical flaw
which makes an argument unsound or invalid.
(Note that you can criticize more than just the soundness of an
argument. Arguments are almost always presented with some specific
PURPOSE in mind - and the INTENT of the argument may also be worthy of
criticism.)
Arguments which contain fallacies are described as fallacious. They
often appear valid and convincing; sometimes only close inspection
reveals the logical flaw.
Below is a list of some common fallacies, and also some rhetorical
devices often used in debate. The list isn't intended to be
exhaustive; the hope is that if you learn to recognize some of the
more common fallacies, you'll be able to avoid being fooled by them.
List of fallacies  --------------------------------------------
Accent 
Ad hoc 
Affirmation of the consequent 
Amphiboly 
Anecdotal evidence 
Argumentum ad antiquitatem 
Argumentum ad baculum / Appeal to force 
Argumentum ad crumenam 
Argumentum ad hominem 
Argumentum ad ignorantiam 
Argumentum ad lazarum 
Argumentum ad logicam 
Argumentum ad misericordiam 
Argumentum ad nauseam 
Argumentum ad novitatem 
Argumentum ad numerum 
Argumentum ad populum 
Argumentum ad verecundiam 
Audiatur et altera pars 
Bifurcation 
Circulus in demonstrando 
Complex question / Fallacy of interrogation / Fallacy of
presupposition 
Composition 
Converse accident / Hasty generalization 
Converting a conditional 
Cum hoc ergo propter hoc 
Denial of the antecedent 
Dicto simpliciter / The fallacy of accident / Sweeping generalization 
Division 
Equivocation / Fallacy of four terms 
Extended analogy 
Ignoratio elenchi / Irrelevant conclusion 
Natural Law fallacy / Appeal to Nature 
"No True Scotsman ..." fallacy 
Non causa pro causa 
Non sequitur 
Petitio principii / Begging the question 
Plurium interrogationum / Many questions 
Post hoc, ergo propter hoc 
Red herring 
Reification / Hypostatization 
Shifting the burden of proof 
Slippery slope argument 
Straw man 
Tu quoque 
Undistributed Middle / "A is based on B" fallacies / "... is a type of
..." fallacies 
--------------------------------------------------------------------------------
Accent 
Accent is a form of fallacy through shifting meaning. In this case,
the meaning is changed by altering which parts of a statement are
emphasized. For example:
"We should not speak ill of our friends"
and
"We should not speak ill of our friends"
Be particularly wary of this fallacy on the net, where it's easy to
misread the emphasis of what's written.
Ad hoc (for this purpose only)
As mentioned earlier, there is a difference between argument and
explanation. If we're interested in establishing A, and B is offered
as evidence, the statement "A because B" is an argument. If we're
trying to establish the truth of B, then "A because B" is not an
argument, it's an explanation.
The Ad Hoc fallacy is to give an after-the-fact explanation which
doesn't apply to other situations. Often this ad hoc explanation will
be dressed up to look like an argument. For example, if we assume that
God treats all people equally, then the following is an ad hoc
explanation:
"I was healed from cancer."
"Praise the Lord, then. He is your healer."
"So, will He heal others who have cancer?"
"Er... The ways of God are mysterious."
Affirmation of the consequent
This fallacy is an argument of the form "A implies B, B is true,
therefore A is true." To understand why it is a fallacy, examine the
truth table for implication given earlier. Here's an example:
"If the universe had been created by a supernatural being, we would
see order and organization everywhere. And we do see order, not
randomness--so it's clear that the universe had a creator."
This is the converse of Denial of the Antecedent.
Amphiboly
Amphiboly occurs when the premises used in an argument are ambiguous
because of careless or ungrammatical phrasing. For example:
"Premise: Belief in God fills a much-needed gap."
Anecdotal evidence
One of the simplest fallacies is to rely on anecdotal evidence. For
example:
"There's abundant proof that God exists and is still performing
miracles today. Just last week I read about a girl who was dying of
cancer. Her whole family went to church and prayed for her, and she
was cured."
It's quite valid to use personal experience to illustrate a point; but
such anecdotes don't actually prove anything to anyone. Your friend
may say he met Elvis in the supermarket, but those who haven't had the
same experience will require more than your friend's anecdotal
evidence to convince them.
Anecdotal evidence can seem very compelling, especially if the
audience wants to believe it. This is part of the explanation for
urban legends; stories which are verifiably false have been known to
circulate as anecdotes for years.
Argumentum ad antiquitatem
This is the fallacy of asserting that something is right or good
simply because it's old, or because "that's the way it's always been."
The opposite of Argumentum ad Novitatem.
"For thousands of years Christians have believed in Jesus Christ.
Christianity must be true, to have persisted so long even in the face
of persecution."
Argumentum ad baculum (Appeal to force or fear)
An Appeal to Force happens when someone resorts to force (or the
threat of force) to try and push others to accept a conclusion. This
fallacy is often used by politicians, and can be summarized as "might
makes right." The threat doesn't have to come directly from the person
arguing. For example:
"Thus there is ample proof of the truth of the Bible. All those who
refuse to accept that truth will burn in Hell."
"In any case, I know your phone number and I know where you live. Have
I mentioned I am licensed to carry concealed weapons?"
Argumentum ad crumenam
The fallacy of believing that money is a criterion of correctness;
that those with more money are more likely to be right. The opposite
of Argumentum ad Lazarum. Example:
"Microsoft software is undoubtedly superior; why else would Bill Gates
have gotten so rich?"
Argumentum ad hominem (Abusive: attacking the person)
Argumentum ad hominem literally means "argument directed at the man";
there are two varieties.
The first is the abusive form. If you refuse to accept a statement,
and justify your refusal by criticizing the person who made the
statement, then you are guilty of abusive argumentum ad hominem. For
example:
"You claim that atheists can be moral--yet I happen to know that you
abandoned your wife and children."
This is a fallacy because the truth of an assertion doesn't depend on
the virtues of the person asserting it. A less blatant argumentum ad
hominem is to reject a proposition based on the fact that it was also
asserted by some other easily criticized person. For example:
"Therefore we should close down the church? Hitler and Stalin would
have agreed with you."
A second form of argumentum ad hominem is to try and persuade someone
to accept a statement you make, by referring to that person's
particular circumstances. For example:
"Therefore it is perfectly acceptable to kill animals for food. I hope
you won't argue otherwise, given that you're quite happy to wear
leather shoes."
This is known as circumstantial argumentum ad hominem. The fallacy can
also be used as an excuse to reject a particular conclusion. For
example:
"Of course you'd argue that positive discrimination is a bad thing.
You're white."
This particular form of Argumentum ad Hominem, when you allege that
someone is rationalizing a conclusion for selfish reasons, is also
known as "poisoning the well."
It's not always invalid to refer to the circumstances of an individual
who is making a claim. If someone is a known perjurer or liar, that
fact will reduce their credibility as a witness. It won't, however,
prove that their testimony is false in this case. It also won't alter
the soundness of any logical arguments they may make.
Argumentum ad ignorantiam (Argument from ignorance)
Argumentum ad ignorantiam means "argument from ignorance." The fallacy
occurs when it's argued that something must be true, simply because it
hasn't been proved false. Or, equivalently, when it is argued that
something must be false because it hasn't been proved true.
(Note that this isn't the same as assuming something is false until it
has been proved true. In law, for example, you're generally assumed
innocent until proven guilty.)
Here are a couple of examples:
"Of course the Bible is true. Nobody can prove otherwise."
"Of course telepathy and other psychic phenomena do not exist. Nobody
has shown any proof that they are real."
In scientific investigation, if it is known that an event would
produce certain evidence of its having occurred, the absence of such
evidence can validly be used to infer that the event didn't occur. It
does not prove it with certainty, however.
For example:
"A flood as described in the Bible would require an enormous volume of
water to be present on the earth. The earth doesn't have a tenth as
much water, even if we count that which is frozen into ice at the
poles. Therefore no such flood occurred."
It is, of course, possible that some unknown process occurred to
remove the water. Good science would then demand a plausible testable
theory to explain how it vanished.
Of course, the history of science is full of logically valid bad
predictions. In 1893, the Royal Academy of Science were convinced by
Sir Robert Ball that communication with the planet Mars was a physical
impossibility, because it would require a flag as large as Ireland,
which it would be impossible to wave. [Fortean Times Number 82.]
See also Shifting the Burden of Proof.
Argumentum ad lazarum
The fallacy of assuming that someone poor is sounder or more virtuous
than someone who's wealthier. This fallacy is the opposite of the
Argumentum ad Crumenam. For example:
"Monks are more likely to possess insight into the meaning of life, as
they have given up the distractions of wealth."
Argumentum ad logicam
This is the "fallacy fallacy" of arguing that a proposition is false
because it has been presented as the conclusion of a fallacious
argument. Remember always that fallacious arguments can arrive at true
conclusions.
"Take the fraction 16/64. Now, canceling a six on top and a six on the
bottom, we get that 16/64 = 1/4."
"Wait a second! You can't just cancel the six!"
"Oh, so you're telling us 16/64 is not equal to 1/4, are you?"
Argumentum ad misericordiam (Appeal to pity; Special pleading)
This is the Appeal to Pity, also known as Special Pleading. The
fallacy is committed when someone appeals to pity for the sake of
getting a conclusion accepted. For example:
"I did not murder my mother and father with an axe! Please don't find
me guilty; I'm suffering enough through being an orphan."
Argumentum ad nauseam
This is the incorrect belief that an assertion is more likely to be
true, or is more likely to be accepted as true, the more often it is
heard. So an Argumentum ad Nauseam is one that employs constant
repetition in asserting something; saying the same thing over and over
again until you're sick of hearing it.
On the Net, your argument is often less likely to be heard if you
repeat it over and over again, as people will tend to put you in their
kill files.
Argumentum ad novitatem
This is the opposite of the Argumentum ad Antiquitatem; it's the
fallacy of asserting that something is better or more correct simply
because it is new, or newer than something else.
"BeOS is a far better choice of operating system than OpenStep, as it
has a much newer design."
Argumentum ad numerum
This fallacy is closely related to the argumentum ad populum. It
consists of asserting that the more people who support or believe a
proposition, the more likely it is that that proposition is correct.
For example:
"The vast majority of people in this country believe that capital
punishment has a noticeable deterrent effect. To suggest that it
doesn't in the face of so much evidence is ridiculous."
"All I'm saying is that thousands of people believe in pyramid power,
so there must be something to it."
Argumentum ad populum (Appeal to the people or gallery)
This is known as Appealing to the Gallery, or Appealing to the People.
You commit this fallacy if you attempt to win acceptance of an
assertion by appealing to a large group of people. This form of
fallacy is often characterized by emotive language. For example:
"Pornography must be banned. It is violence against women."
"For thousands of years people have believed in Jesus and the Bible.
This belief has had a great impact on their lives. What more evidence
do you need that Jesus was the Son of God? Are you trying to tell
those people that they are all mistaken fools?"
Argumentum ad verecundiam (Appeal to authority)
The Appeal to Authority uses admiration of a famous person to try and
win support for an assertion. For example:
"Isaac Newton was a genius and he believed in God."
This line of argument isn't always completely bogus when used in an
inductive argument; for example, it may be relevant to refer to a
widely-regarded authority in a particular field, if you're discussing
that subject. For example, we can distinguish quite clearly between:
"Hawking has concluded that black holes give off radiation"
and
"Penrose has concluded that it is impossible to build an intelligent
computer"
Hawking is a physicist, and so we can reasonably expect his opinions
on black hole radiation to be informed. Penrose is a mathematician, so
it is questionable whether he is well-qualified to speak on the
subject of machine intelligence.
Audiatur et altera pars
Often, people will argue from assumptions which they don't bother to
state. The principle of Audiatur et Altera Pars is that all of the
premises of an argument should be stated explicitly. It's not strictly
a fallacy to fail to state all of your assumptions; however, it's
often viewed with suspicion.
Bifurcation
Also referred to as the "black and white" fallacy and "false
dichotomy," bifurcation occurs if someone presents a situation as
having only two alternatives, where in fact other alternatives exist
or can exist. For example:
"Either man was created, as the Bible tells us, or he evolved from
inanimate chemicals by pure random chance, as scientists tell us. The
latter is incredibly unlikely, so ..."
Circulus in demonstrando
This fallacy occurs if you assume as a premise the conclusion which
you wish to reach. Often, the proposition is rephrased so that the
fallacy appears to be a valid argument. For example:
"Homosexuals must not be allowed to hold government office. Hence any
government official who is revealed to be a homosexual will lose his
job. Therefore homosexuals will do anything to hide their secret, and
will be open to blackmail. Therefore homosexuals cannot be allowed to
hold government office."
Note that the argument is entirely circular; the premise is the same
as the conclusion. An argument like the above has actually been cited
as the reason for the British Secret Services' official ban on
homosexual employees.
Circular arguments are surprisingly common, unfortunately. If you've
already reached a particular conclusion once, it's easy to
accidentally make it an assertion when explaining your reasoning to
someone else.
Complex question / Fallacy of interrogation / Fallacy of
presupposition
This is the interrogative form of Begging the Question. One example is
the classic loaded question:
"Have you stopped beating your wife?"
The question presupposes a definite answer to another question which
has not even been asked. This trick is often used by lawyers in
cross-examination, when they ask questions like:
"Where did you hide the money you stole?"
Similarly, politicians often ask loaded questions such as:
"How long will this EU interference in our affairs be allowed to
continue?"
or
"Does the Chancellor plan two more years of ruinous privatization?"
Another form of this fallacy is to ask for an explanation of something
which is untrue or not yet established.
Composition
The Fallacy of Composition is to conclude that a property shared by a
number of individual items, is also shared by a collection of those
items; or that a property of the parts of an object, must also be a
property of the whole thing. Examples:
"The bicycle is made entirely of low mass components, and is therefore
very lightweight."
"A car uses less petrochemicals and causes less pollution than a bus.
Therefore cars are less environmentally damaging than buses."
A related form of fallacy of composition is the "just" fallacy, or
fallacy of mediocrity. This is the fallacy that assumes that any given
member of a set must be limited to the attributes that are held in
common with all the other members of the set. Example:
"Humans are just animals, so we should not concern ourselves with
justice; we should just obey the law of the jungle."
Here the fallacy is to reason that because we are animals, we can have
only properties which animals have; that nothing can distinguish us as
a special case.
Converse accident / Hasty generalization
This fallacy is the reverse of the Fallacy of Accident. It occurs when
you form a general rule by examining only a few specific cases which
aren't representative of all possible cases. For example:
"Jim Bakker was an insincere Christian. Therefore all Christians are
insincere."
Converting a conditional
This fallacy is an argument of the form "If A then B, therefore if B
then A."
"If educational standards are lowered, the quality of argument seen on
the Net worsens. So if we see the level of debate on the net get worse
over the next few years, we'll know that our educational standards are
still falling."
This fallacy is similar to the Affirmation of the Consequent, but
phrased as a conditional statement.
Cum hoc ergo propter hoc
This fallacy is similar to post hoc ergo propter hoc. The fallacy is
to assert that because two events occur together, they must be
causally related. It's a fallacy because it ignores other factors that
may be the cause(s) of the events.
"Literacy rates have steadily declined since the advent of television.
Clearly television viewing impedes learning."
This fallacy is a special case of the more general non causa pro
causa.
Denial of the antecedent
This fallacy is an argument of the form "A implies B, A is false,
therefore B is false." The truth table for implication makes it clear
why this is a fallacy.
Note that this fallacy is different from Non Causa Pro Causa. That has
the form "A implies B, A is false, therefore B is false," where A does
not in fact imply B at all. Here, the problem isn't that the
implication is invalid; rather it's that the falseness of A doesn't
allow us to deduce anything about B.
"If the God of the Bible appeared to me, personally, that would
certainly prove that Christianity was true. But God has never appeared
to me, so the Bible must be a work of fiction."
This is the converse of the fallacy of Affirmation of the Consequent.
Dicto simpliciter / Fallacy of accident / Sweeping generalization 
A sweeping generalization occurs when a general rule is applied to a
particular situation, but the features of that particular situation
mean the rule is inapplicable. It's the error made when you go from
the general to the specific. For example:
"Christians generally dislike atheists. You are a Christian, so you
must dislike atheists."
This fallacy is often committed by people who try to decide moral and
legal questions by mechanically applying general rules.
Division
The fallacy of division is the opposite of the Fallacy of Composition.
It consists of assuming that a property of some thing must apply to
its parts; or that a property of a collection of items is shared by
each item.
"You are studying at a rich college. Therefore you must be rich."
"Ants can destroy a tree. Therefore this ant can destroy a tree."
Equivocation / Fallacy of four terms
Equivocation occurs when a key word is used with two or more different
meanings in the same argument. For example:
"What could be more affordable than free software? But to make sure
that it remains free, that users can do what they like with it, we
must place a license on it to make sure that will always be freely
redistributable."
One way to avoid this fallacy is to choose your terminology carefully
before beginning the argument, and avoid words like "free" which have
many meanings.
Extended analogy
The fallacy of the Extended Analogy often occurs when some suggested
general rule is being argued over. The fallacy is to assume that
mentioning two different situations, in an argument about a general
rule, constitutes a claim that those situations are analogous to each
other.
Here's real example from an online debate about anti-cryptography
legislation:
"I believe it is always wrong to oppose the law by breaking it."
"Such a position is odious: it implies that you would not have
supported Martin Luther King."
"Are you saying that cryptography legislation is as important as the
struggle for Black liberation? How dare you!"
Ignoratio elenchi / Irrelevant conclusion
The fallacy of Irrelevant Conclusion consists of claiming that an
argument supports a particular conclusion when it is actually
logically nothing to do with that conclusion.
For example, a Christian may begin by saying that he will argue that
the teachings of Christianity are undoubtedly true. If he then argues
at length that Christianity is of great help to many people, no matter
how well he argues he will not have shown that Christian teachings are
true.
Sadly, these kinds of irrelevant arguments are often successful,
because they make people to view the supposed conclusion in a more
favorable light.
Natural Law fallacy / Appeal to Nature
The Appeal to Nature is a common fallacy in political arguments. One
version consists of drawing an analogy between a particular
conclusion, and some aspect of the natural world--and then stating
that the conclusion is inevitable, because the natural world is
similar:
"The natural world is characterized by competition; animals struggle
against each other for ownership of limited natural resources.
Capitalism, the competitive struggle for ownership of capital, is
simply an inevitable part of human nature. It's how the natural world
works."
Another form of appeal to nature is to argue that because human beings
are products of the natural world, we must mimic behavior seen in the
natural world, and that to do otherwise is "unnatural":
"Of course homosexuality is unnatural. When's the last time you saw
two animals of the same sex mating?"
An example of "Appeal to Nature" taken to extremes is The Unabomber
Manifesto.
"No True Scotsman ..." fallacy
Suppose I assert that no Scotsman puts sugar on his porridge. You
counter this by pointing out that your friend Angus likes sugar with
his porridge. I then say "Ah, yes, but no true Scotsman puts sugar on
his porridge.
This is an example of an ad hoc change being used to shore up an
assertion, combined with an attempt to shift the meaning of the words
used original assertion; you might call it a combination of fallacies.
Non causa pro causa
The fallacy of Non Causa Pro Causa occurs when something is identified
as the cause of an event, but it has not actually been shown to be the
cause. For example:
"I took an aspirin and prayed to God, and my headache disappeared. So
God cured me of the headache."
This is known as a false cause fallacy. Two specific forms of non
causa pro causa fallacy are the cum hoc ergo propter hoc and post hoc
ergo propter hoc fallacies.
Non sequitur
A non sequitur is an argument where the conclusion is drawn from
premises which aren't logically connected with it. For example:
"Since Egyptians did so much excavation to construct the pyramids,
they were well versed in paleontology."
(Non sequiturs are an important ingredient in a lot of humor. They're
still fallacies, though.)
Petitio principii (Begging the question)
This fallacy occurs when the premises are at least as questionable as
the conclusion reached. Typically the premises of the argument
implicitly assume the result which the argument purports to prove, in
a disguised form. For example:
"The Bible is the word of God. The word of God cannot be doubted, and
the Bible states that the Bible is true. Therefore the Bible must be
true.
Begging the question is similar to circulus in demonstrando, where the
conclusion is exactly the same as the premise.
Plurium interrogationum / Many questions
This fallacy occurs when someone demands a simple (or simplistic)
answer to a complex question.
"Are higher taxes an impediment to business or not? Yes or no?"
Post hoc ergo propter hoc
The fallacy of Post Hoc Ergo Propter Hoc occurs when something is
assumed to be the cause of an event merely because it happened before
that event. For example:
"The Soviet Union collapsed after instituting state atheism. Therefore
we must avoid atheism for the same reasons."
This is another type of false cause fallacy.
Red herring
This fallacy is committed when someone introduces irrelevant material
to the issue being discussed, so that everyone's attention is diverted
away from the points made, towards a different conclusion.
"You may claim that the death penalty is an ineffective deterrent
against crime--but what about the victims of crime? How do you think
surviving family members feel when they see the man who murdered their
son kept in prison at their expense? Is it right that they should pay
for their son's murderer to be fed and housed?"
Reification / Hypostatization
Reification occurs when an abstract concept is treated as a concrete
thing.
"I noticed you described him as 'evil.' Where does this 'evil' exist
within the brain? You can't show it to me, so I claim it doesn't
exist, and no man is 'evil.'"
Shifting the burden of proof
The burden of proof is always on the person asserting something.
Shifting the burden of proof, a special case of Argumentum ad
Ignorantiam, is the fallacy of putting the burden of proof on the
person who denies or questions the assertion. The source of the
fallacy is the assumption that something is true unless proven
otherwise.
For further discussion of this idea, see the "Introduction to Atheism"
document.
"OK, so if you don't think the grey aliens have gained control of the
US government, can you prove it?"
Slippery slope argument
This argument states that should one event occur, so will other
harmful events. There is no proof made that the harmful events are
caused by the first event. For example:
"If we legalize marijuana, then more people would start to take crack
and heroin, and we'd have to legalize those too. Before long we'd have
a nation full of drug-addicts on welfare. Therefore we cannot legalize
marijuana."
Straw man
The straw man fallacy is when you misrepresent someone else's position
so that it can be attacked more easily, knock down that misrepresented
position, then conclude that the original position has been
demolished. It's a fallacy because it fails to deal with the actual
arguments that have been made.
"To be an atheist, you have to believe with absolute certainty that
there is no God. In order to convince yourself with absolute
certainty, you must examine all the Universe and all the places where
God could possibly be. Since you obviously haven't, your position is
indefensible."
The above straw man argument appears at about once a week on the net.
If you can't see what's wrong with it, read the "Introduction to
Atheism" document.
Tu quoque
This is the famous "you too" fallacy. It occurs if you argue that an
action is acceptable because your opponent has performed it. For
instance:
"You're just being randomly abusive."
"So? You've been abusive too."
This is a personal attack, and is therefore a special case of
Argumentum ad Hominem.
Undistributed Middle / "A is based on B" fallacies / "... is a type of
..." fallacies
These fallacies occur if you attempt to argue that things are in some
way similar, but you don't actually specify in what way they are
similar. Examples:
"Isn't history based upon faith? If so, then isn't the Bible also a
form of history?"
"Islam is based on faith, Christianity is based on faith, so isn't
Islam a form of Christianity?"
"Cats are a form of animal based on carbon chemistry, dogs are a form
of animal based on carbon chemistry, so aren't dogs a form of cat?"