monty python and the quest for the perfect fallacy - arranged by valerie d. van curen
TRANSCRIPT
MONTY PYTHON AND
THE QUEST FOR THE PERFECT
FALLACY
The Witch’s Trial Argument
Activity adapted from Annenberg Classroom Fact Check
FactCheckEd.org
THE ARGUMENT
A L L W I T C H E S A R E T H I N G S T H A T C A N B U R N.
A L L T H I N G S T H A T C A N B U R N
A R E M A D E O F W O O D.
T H E R E F O R E , A L L W I T C H E S
A R E M A D E O F W O O D.
A L L T H I N G S T H A T A R E M A D E O F W O O D
A R E T H I N G S T H A T C A N F L OA T.
A L L T H I N G S T H A T W E I G H A S M U C H A S A
D U C K A R E T H I N G S T H A T C A N F L OA T.
S O , A L L T H I N G S T H A T W E I G H A S M U C H A S A
D U C K A R E T H I N G S T H A T A R E M A D E O F W O O D.
T H E R E F O R E , A L L W I T C H E S A R E T H I N G S
T H A T W E I G H A S M U C H A S A D U C K .
T H I S I S A T H I N G T H A T
W E I G H S A S M U C H A S A D U C K .
T H E R E F O R E , T H I S T H I N G I S A W I T C H .
FIRST ARGUMENT PART
All witches are things that can burn.
All things that can burn are made of wood.
Therefore, all witches are made of wood.
Is this a valid argument?
THIS IS A VALID ARGUMENT.
That is, (3) really does follow logically from
(1) and (2).
That’s not to say that it’s an especially
convincing argument because premise (2) is
rather obviously false.
Still, if (2) were true, then the conclusion
would have to be true as well.
So this step is valid but unsound.
1. All witches are things
that can burn.
2. All things that can
burn are made of wood.
3. Therefore, all witches
are made of wood.
SECOND ARGUMENT PART
All things that are made of wood are things that can float.
All things that weigh as much as a duck are things that can float.
So, All things that weigh as much as a duck are things that are
made of wood.
Is this a valid argument?
THIS IS A FALLACY
This argument commits the fallacy of the
undistributed middle.
The structure of the argument is the old
familiar
• All A is C.
• All B is C.
• Therefore, all A is B.
And that, of course, isn’t a valid argument.
A. All things that are made of
wood are things that can float.
B. All things that weigh as much as
a duck are things that can float.
C. So, All things that weigh as
much as a duck are things that
are made of wood.
THIRD ARGUMENT PART
Therefore, all witches are made of wood.
So all things that weigh as much as a duck are things that are made
of wood.
Therefore, all witches are things that weigh as much as a duck.
Is this a valid argument?
THIS IS A FALLACY
This argument has the same
problem as the second argument.
It’s also an undistributed middle.
• All A is C.
• All B is C.
• Therefore, all A is B.
All witches are made of wood.
So all things that weigh as much
as a duck are things that are made
of wood.
Therefore, all witches are things
that weigh as much as a duck.
FINAL ARGUMENT PART
All witches are things that weigh as much as a duck.
This thing is a thing that weighs as much as a duck.
Therefore, this thing is a witch.
Is this a valid argument?
THIS IS A FALLACY
The final argument:
Yes, once again, it’s an undistributed
middle .
All A is C.
All B is C.
Therefore, all A is B.
All witches are things that weigh
as much as a duck.
This thing is a thing that weighs
as much as a duck.
Therefore, this thing is a witch.