This article is from the Atheism FAQ, by mathew firstname.lastname@example.org with numerous contributions by others.
The 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."
"A is based on B" fallacies / "...is a type of..." fallacies / Fallacy of
the Undistributed Middle
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
"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
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 I fall into the swimming pool, I get wet. I am wet, so I must
have fallen into the swimming pool."
This is the converse of Denial of the Antecedent.
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 I fall into the swimming pool, I get wet. I did not fall into
the swimming pool, therefore I am not wet."
This is the converse of the fallacy of Affirmation of the Consequent.
Converting a conditional
This fallacy is an argument of the form "If A then B, therefore if B
"If educational standards are lowered, the quality of argument seen
on the Internet 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."
"If it's raining outside and I don't have an umbrella I get wet. So
if I get wet, then it's raining outside and I don't have an
This fallacy is similar to the Affirmation of the Consequent, but
phrased as a conditional statement.
Also referred to as the "black and white" fallacy, bifurcation occurs
if you present a situation as having only two alternatives, where in
fact other alternatives exist or can exist.
Plurium interrogationum / Many questions
This fallacy occurs when someone demands a simple (or simplistic)
answer to a complex question.
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."
(Personally, I rather enjoy reading examples of this fallacy. A really
good non sequitur can cause the 'boggle' response, or even make me
burst out laughing. Indeed, non sequiturs are an important ingredient
in a lot of humour. They're still fallacies, though.)
This fallacy is committed when someone introduces irrelevant material
to the issue being discussed, so that everyone else's attention is
diverted away from the points made, towards a different conclusion.
Reification / Hypostatization
Reification occurs when an abstract concept is treated as a concrete