Here’s how to catch another common “if-then”
fallacy.
Welcome to Critical Thinking Scan, where we
look at how you can think about any faith-challenging
message and arrive at a biblical, logical
conclusion yourself.
I’m Patricia Engler and today, let’s look
at another type of formal fallacy, or invalid
form of logic, called denying the antecedent.
This is another faulty type of conditional
argument, and as we’ve been talking about
in the last couple of episodes, conditional
arguments are based on “if-then” statements,
like “If you have a dog, then you are a
pet owner.”
Remember, the IF statement is called the antecedent,
which people often represent with the letter
P, and the THEN statement is called the consequent,
which is often symbolized by the letter Q.
In this case, P is the statement, “You have a dog”
and Q is the statement, “You are a pet owner.”
Now, denying the antecedent means showing
that the “if” statement P, is false in
order to argue that the “then” statement,
Q is also false, using the structure,
“If P, then Q. Not Q, therefore, not P.”
For example, “If you have a dog, then you are a pet owner.
You do not have a dog.
Therefore, you are not a pet owner.”
Does that argument sound reasonable?
No; there are other ways to be a pet owner
besides having a dog.
You might have a cat, or a chinchilla, or
a small hairless aardvark.
So, the conclusion “you are not a pet owner”
does not necessarily follow from the given premises.
And if an argument’s conclusion does not
logically follow from its premises,
that argument is invalid.
Now, you might have noticed that denying the
antecedent is the opposite of the other type
of faulty conditional argument we’ve looked
at, called affirming the consequent.
Both argument structures are invalid if there
are other ways the conclusion could be true,
besides the given premises.
Now, let’s think about some cases where
faith-challenging messages might involve
denying the antecedent.
One example which Dr. Jason Lisle gives in an article 
you can find linked to this video, goes like this:
“If we found dinosaurs and
humans next to each other in the same rock
formation, then they must have lived at the
same time.
We do not find them next to each other in
the same rock formation.
Therefore, they did not live at the same time.”
This argument might sound persuasive, but it’s logically 
invalid, because it denies the antecedent.
There could be other reasons we don’t typically
find human and dinosaur fossils together,
as you can learn from the linked resources.
For example, dinosaurs and humans may not
normally have lived in close proximity.
Or, humans may have initially been better
equipped than many dinosaurs to escape the
rising waters of the global flood described
in Genesis, which would have buried most of
the dinosaur fossils we can find today.
As another example, here’s a form of denying
the antecedent which one of my textbooks basically
accused creationists of using.
It said that creationists say:
“If we observe one kind of living thing changing 
into another, then evolution is true.
We do not observe one kind of living thing
changing into another.
Therefore, evolution is not true.”
And worded like that, this IS a fallacy, IF
it implies that the ONLY way for evolution
to be true is if we can directly observe it.
And as my textbook pointed out that there
are other ways to confirm something is happening
besides directly observing it.
So, is it a fallacy to say evolution is false
because we don’t directly observe one kind
of thing changing into another?
Not if we show WHY we don’t observe it.
Like you can learn from the linked resources,
mechanisms like mutation and natural selection
do not produce the functional new genetic
information required to evolve one kind of
creature into another.
So, a better way to present this argument
is, “Only if natural processes can explain
the origin of living things’ genetic information
is evolution remotely possible.
What we do observe of natural processes completely
opposes this idea.
Therefore, evolution is extremely unlikely.”
This argument still denies the antecedent,
“natural processes can explain new information.”
But by showing there is no other way for the consequent, 
“evolution is true” to be true without that antecedent,
the argument is no longer a fallacy.
For more on how to think critically about
any faith-challenging messages, you can access
my other CT Scan episodes packed with tactics,
tips and tools that helped me as a Christian
student in secular university.
Thank you for watching!
Hey – It’s Patricia.
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