Logical Fallacies 101
Adam vanLangenberg
MSSS
Ad ignorantiam
Claiming that something is true
because we can’t disprove it.
“We don’t know what those lights in the sky are, therefore they are aliens.”
Argument
from authority
The idea that something must be true
because it has been said by somebody
with authority.
“I use these magical healing crystals every day!” – Dr S. Novella, M.D.
Argument from
Final Consequences
Making an argument based on how
good/bad the consequences are.
“Aliens must exist because otherwise we would be all alone in the universe.”
Argument from
Personal Incredulity
Claiming that something is impossible because
you personally don’t understand it.
“I don’t understand how evolution works so there must be an intelligent
designer.”
Argument from
Antiquity
Stating that something must be good
because it has been used for a long
time.
“Of course it’s legitimate! Cave men have been doing this for millions of
years!”
Argument from
Popularity
Stating that something must be
legitimate because a lot of people
believe in it.
“1 million Usher fans can’t be wrong!”
Correlation
vs. Causation
Assuming cause and effect for two
things simply because they occurred
together.
“I have never been attacked by a bear while wearing this tie. Bear-proof tie!”
Unexplained vs.
Unexplainable
Believing that because we cannot explain some
phenomenon now, we will never be able to
explain it.
“We don’t know what the Voynich Manuscript means so it must have been
written by angels!”
False Continuum
Thinking that because no distinct line
exists between two extremes, then those
two extremes are really the same thing.
“There’s a fuzzy line between religions and cults, so all religions must be
cults.”
False Dichotomy
Insisting that things must either be
one way or another.
“Either you are with us, or you are with the terrorists.”
Inconsistency
Applying criteria to one thing but not
to another.
“Prescription drugs need to be strongly regulated but herbal supplements do
not.”
Non-Sequitur
Making a conclusion that doesn’t
follow from the arguments.
“God is love. Love is blind. Ray Charles is blind. Therefore Ray Charles is
God.
Post-hoc ergo
propter hoc
Saying that because A happened
before B, A must have caused B.
“A rooster crows before the sun rises so the rooster’s crowing must cause the
sun to rise. Clever rooster!”
Reductio ad absurdim
Extending an argument to an absurd
conclusion.
“If you don’t believe in aliens because you haven’t seen one, how can you
believe in France? You haven’t seen it either.”
Ad hominem
(My favourite)
Attacking a person, rather than their
claims.
“Your argument is wrong because you’re a big fatty fat fat.”
Slippery slope
Arguing that believing something must
also involve believing in its extreme.
“If you support the death penalty then you must also support genocide.”
Special pleading
Arbitrarily introducing something
into an argument to make it work.
“My psychic powers didn’t work because of all the sceptics in the room! Also,
because of magnetic interference.”
Straw man
Twisting your opponent’s argument
to make it easier to argue against.
“I think homeopathy is stupid and should be banned.”
“So you think we should ban medicines, do you?”
Tautology
The argument that A = B
because A = B.
“Go to bed.”
“Why?”
“Because I said so.”
Moving the
goalpost
After losing an argument, throwing
something else into the ring which
cannot yet be proven.
“…and that is why your mother is fat.”
“Oh yeah? Well then what is she eating right now?”
Tu quoque
Attacking somebody for arguing against
something that they used to do.
“You can’t say murder is wrong, you’re a serial killer!”
Begging the question
Not stating something important that
your argument assumes.
“It is McDonald’s fault that I am fat!”