CRITICAL THINKING – Fallacies: Denying The Antecedent



(intro music) Hello, I'm Matthew Harris. I'm a philosophy graduate[br]student at Duke University, and today I'll be discussing the formal fallacy of[br]denying the antecedent. Denying the antecedent[br]is a formal fallacy, meaning that the argument has a flaw contained in its logical form. This is important because whenever this pattern of argument occurs, regardless of topic or content, the argument will always be invalid. So how can we tell when the fallacy of denying[br]the antecedent occurs? Well, it happens when we mistake the direction of a conditional, or confuse it for a biconditional. And it starts with the denial of the conditional statement's antecedent, then concludes the[br]denial of its consequent. The logical form of arguments that commit the fallacy of denying the[br]antecedent look like this: "If P, then Q. "Not P. Therefore, not Q." Now, let's take a look[br]at this conditional: "If you are a ski instructor,[br]then you have a job." The antecedent statement[br]of this conditional is "you are a ski instructor," and the consequent is "you have a job." But suppose someone made an argument with this conditional[br]as its first premise. Premise (1): If you are a ski[br]instructor, then you have a job. Premise (2): But you are[br]not a ski instructor. Conclusion: Therefore,[br]you do not have a job. Here, the second premise is[br]a denial of the antecedent. This premise does not tell us that only ski instructors have jobs. So, even if the conditional[br]statement is true (that ski instructors have jobs), it cannot be inferred that if[br]you are not a ski instructor, then you are unemployed. A conditional could validly be used to argue for the[br]truth of this consequent by affirming the antecedent. We find this in the arguments of a form called "modus ponens." It is also valid to argue from[br]the denial of a consequent to a denial of the antecedent. But it is never, ever valid[br]to deny the antecedent to reject its consequent. Let's try another example: "If you are a property[br]owner, then you are a human. "But you are not a property owner. "Therefore, you are not a human." The antecedent, that you are a property owner, is being denied. Even though you need to be[br]a human to own property, this has no bearing on humans who do not own property at all. For example, graduate students. Let's consider one last example: "If anyone is watching this video, "then they are on the internet. "Some people are not watching this video. "Therefore, they are not on the internet." Again, denying the antecedent by pointing out that not everyone is currently watching this video does not validly demonstrate[br]the denial of the consequent, that they're not on the internet at all. These have been a few cases[br]that I hope will come in handy in avoiding this formal[br]fallacy in your own arguments. For more related to the fallacy[br]of denying the antecedent, I recommend that you take a[br]look at the other related videos on informal and formal fallacies, the fallacy of affirming the[br]consequent, and conditionals. Subtitles by the Amara.org community

23 thoughts on “CRITICAL THINKING – Fallacies: Denying The Antecedent”

  1. What if you write
    P1: Only if you are a ski instructor then you have a job
    P2: You are not s ski instructor

    C: Therefore you do not have a job

    This is a valid argument with denying the antecedent

  2. Premise 1: If you are a property owner, then you are a human
    Premise 2: You are not a property owner
    Conclusion: You are not a human

    The top definition of property is: that which a person owns; the possession or possessions of a particular owner. Isn't a person's body their property then? Premise 2 is false by definition.

  3. Why not just use much simpler language and say there's a contradiction in the premises?  Since you don't have well-formed premises, you don't have an argument.  Denying the antecedent – you don't need yet another definition for that.

  4. Great video! Well explained with good examples. That being said, the great content and visual production on this channel would really benefit from getting the audio up to the same standard. The voice channel on this video sounds like it was recorded with a cheap mic in a booming, echo-y room. It should be easy to find someone on campus with a good setup for recording the voiceover, and I'm sure they'd be happy to help. Keep up the good work!

  5. Man you guys are wasting a crap ton of money for a bullshit non-education. Not to mention this is not true all of the time.. i'm assuming there is some political motive here as is usually the case with pretentious liberals.

  6. Can someone help me out on this one? Is the following argument considered valid?

    If you have a current password, then you can log into the network
    You can't log into the network
    Therefore you don't have a current password.

    And the following invalid?

    If you have a current password, then you can log into the network
    You don't have a current password.
    Therefore you can't log into the network

  7. When the antecedent is denied, what can be said about the consequent? is it unanswerable? is more data needed? is it useless?

  8. Can someone explain to me how this is invalid.

    If you commit the crime, then you should do the time.
    You have not commit the crime
    Therefore you shouldn't be punished (do the time).

    I understand this is a Denying the Antecedent Fallacy but I don't understand why within solely the contents of this argument it is wrong.

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