Critical Thinking Fallacy: Denying The Antecedent
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0:00 - 0:05(intro music)
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0:06 - 0:08Hello, I'm Matthew Harris.
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0:08 - 0:10I'm a philosophy graduate
student at Duke University, -
0:10 - 0:11and today I'll be discussing
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0:11 - 0:14the formal fallacy of
denying the antecedent. -
0:14 - 0:16Denying the antecedent
is a formal fallacy, -
0:16 - 0:20meaning that the argument has a flaw
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0:20 - 0:22contained in its logical form.
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0:22 - 0:23This is important because
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0:23 - 0:26whenever this pattern of argument occurs,
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0:26 - 0:27regardless of topic or content,
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0:27 - 0:29the argument will always be invalid.
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0:31 - 0:31So how can we tell when
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0:31 - 0:34the fallacy of denying
the antecedent occurs? -
0:35 - 0:36Well, it happens when we mistake
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0:36 - 0:39the direction of a conditional,
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0:39 - 0:41or confuse it for a biconditional.
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0:43 - 0:44And it starts with the denial of
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0:44 - 0:46the conditional statement's antecedent,
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0:46 - 0:49then concludes the
denial of its consequent. -
0:50 - 0:52The logical form of arguments that commit
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0:52 - 0:56the fallacy of denying the
antecedent look like this: -
0:56 - 0:58"If P, then Q.
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0:58 - 1:01"Not P. Therefore, not Q."
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1:02 - 1:05Now, let's take a look
at this conditional: -
1:05 - 1:09"If you are a ski instructor,
then you have a job." -
1:09 - 1:11The antecedent statement
of this conditional -
1:11 - 1:14is "you are a ski instructor,"
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1:14 - 1:18and the consequent is "you have a job."
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1:18 - 1:19But suppose someone made an argument
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1:19 - 1:22with this conditional
as its first premise. -
1:22 - 1:26Premise (1): If you are a ski
instructor, then you have a job. -
1:26 - 1:30Premise (2): But you are
not a ski instructor. -
1:30 - 1:33Conclusion: Therefore,
you do not have a job. -
1:34 - 1:38Here, the second premise is
a denial of the antecedent. -
1:38 - 1:40This premise does not tell us
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1:40 - 1:42that only ski instructors have jobs.
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1:42 - 1:45So, even if the conditional
statement is true -
1:45 - 1:47(that ski instructors have jobs),
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1:47 - 1:52it cannot be inferred that if
you are not a ski instructor, -
1:52 - 1:54then you are unemployed.
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1:54 - 1:56A conditional could validly
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1:56 - 1:58be used to argue for the
truth of this consequent -
1:58 - 2:01by affirming the antecedent.
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2:01 - 2:02We find this in the arguments
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2:02 - 2:04of a form called "modus ponens."
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2:06 - 2:09It is also valid to argue from
the denial of a consequent -
2:09 - 2:11to a denial of the antecedent.
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2:11 - 2:16But it is never, ever valid
to deny the antecedent -
2:17 - 2:18to reject its consequent.
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2:20 - 2:22Let's try another example:
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2:22 - 2:25"If you are a property
owner, then you are a human. -
2:26 - 2:29"But you are not a property owner.
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2:29 - 2:30"Therefore, you are not a human."
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2:31 - 2:33The antecedent, that you are
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2:33 - 2:36a property owner, is being denied.
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2:36 - 2:39Even though you need to be
a human to own property, -
2:39 - 2:40this has no bearing on humans
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2:40 - 2:43who do not own property at all.
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2:43 - 2:45For example, graduate students.
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2:45 - 2:48Let's consider one last example:
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2:48 - 2:50"If anyone is watching this video,
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2:50 - 2:52"then they are on the internet.
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2:52 - 2:55"Some people are not watching this video.
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2:55 - 2:57"Therefore, they are not on the internet."
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2:57 - 2:59Again, denying the antecedent
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2:59 - 3:01by pointing out that not everyone
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3:01 - 3:03is currently watching this video
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3:03 - 3:06does not validly demonstrate
the denial of the consequent, -
3:06 - 3:09that they're not on the internet at all.
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3:09 - 3:11These have been a few cases
that I hope will come in handy -
3:11 - 3:14in avoiding this formal
fallacy in your own arguments. -
3:14 - 3:17For more related to the fallacy
of denying the antecedent, -
3:17 - 3:20I recommend that you take a
look at the other related videos -
3:20 - 3:23on informal and formal fallacies,
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3:23 - 3:27the fallacy of affirming the
consequent, and conditionals.
- Title:
- Critical Thinking Fallacy: Denying The Antecedent
- Description:
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In this video, Matthew C. Harris (Duke University) explains the fallacy of denying the antecedent, the formal fallacy that arises from inferring the inverse of a conditional statement. He also explains why graduate students might also be humans.
- Video Language:
- English
- Duration:
- 03:37
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