This article is from the Atheism FAQ, by mathew firstname.lastname@example.org with numerous contributions by others.
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
For further discussion of this idea, see the "Introduction to Atheism"
"OK, so if you don't think the grey aliens have gained control of
the US government, can you prove it?"
The straw man fallacy is when you misrepresent someone else's position
so that it can be attacked more easily, then 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
The 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
This fallacy is best explained using a real example from a 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!"
This is the famous "you too" fallacy. It occurs if you argue that an
action is acceptable because your opponent has performed it. For
"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.
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.
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
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
"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."
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
"Take the fraction 16/64. Now, cancelling a 6 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?"
The "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
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.