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Fundamentals: Soundness

Aaron Ancell discusses the philosophical concept of soundness. After reviewing validity, he defines soundness: an argument is sound when it is valid and has all true premises. He reviews a few examples of sound and unsound arguments, and he encourages you to develop sound arguments on your own.

Speaker: Aaron Ancell, Duke University.

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  • hopper jumping style avatar for user Lucas De Oliveira
    So the philosopher must seek the soundness. What more must the philosopher looking for? How happen the process of to philosophize?
    (6 votes)
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  • starky ultimate style avatar for user matthew
    what happens if you have a premise that you aren't sure of the truth value?
    (3 votes)
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    • piceratops ultimate style avatar for user Nicolas Posunko
      1. In such a situation you cannot know for sure every time whether the argument is sound or unsound, but you can decide whether it's valid or invalid by inspecting the reasoning.
      2. You should probably do that anyway because if you should by any chance find that the argument is invalid, then you've also indirectly figured out that it's unsound no matter whether the premises are true/false/I don't know.
      (2 votes)
  • orange juice squid orange style avatar for user Jenny
    So...Validity is necessary for soundness but not sufficient for soundness...right?
    (4 votes)
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  • male robot donald style avatar for user M Ali
    The video is deleted but you can watch it on Youtube if you want to continue..

    (2 votes)
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  • piceratops ultimate style avatar for user Justin Hsieh
    Okay, so is this a sound argument?
    P1) I have hair on my head.
    P2) Being bald means that you have no hair on your head.
    C) Therefore, I am not bald.
    Right? Because the premises are true, and they guarantee the truth of the conclusion. I just want to know whether or not I grasp this concept. Thanks!
    (3 votes)
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  • male robot hal style avatar for user Corey Piper
    I suppose research would be important when making a sound arguments.
    There's no way that you could say that whales are mammals without the help of a zoologist to help you classify exactly what makes a mammal, right?
    (1 vote)
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    • piceratops ultimate style avatar for user ala.luszczak
      Usually (but not always) to verify the truth of a statement, you at least need to know what the terms used in the statement actually mean. Like: mammal, whale or fur. For that, a dictionary will probably be sufficient. In particular, I think that the way we define "a whale" implies that all whales are mammals.

      The other thing is knowing facts about real world, and that's we're zoologists and other scientists are really getting necessary. For example, knowing if the whales have fur, if they eat fish or how big they can get, requires actual observation of animals.

      Thinking more broadly, I would say that arguments often don't relate to objects in real life, which can be easily named and classified (like: whales, mammals, fur), but to more abstract things, that need to be separately defined, as we don't really have a general agreement of what they mean (like: justice, consciousness, well-being, etc.). In such cases, the truth of the premises depends on the definitions that you choose to use, and might not be related to anything a scientist can analyze in physical world.

      Mathematics is a great example: in mathematics everything follows from a very limited set of axioms (assumptions). There is no external research required to validate any premise, as the truth of any premise must follow from the axioms.
      (5 votes)
  • piceratops ultimate style avatar for user Justin Hsieh
    P1) Apples are food.
    P2) All food is edible.
    P3) Anything that is edible, I am able to eat.
    C) Therefore, I am able to eat apples.
    (2 votes)
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  • aqualine ultimate style avatar for user Izzy
    I'd like to just point out that the grasshopper in the video was not wearing a top hat as I would have expected.
    (2 votes)
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  • female robot grace style avatar for user tw486364
    Still thinking about Soundness at pm ...

    1)If elevated emotions ( love, joy,gratitude) have a higher frequency than base emotions ( anger, jealousy, and fear).
    2) If on a higher frequency, you feel like energy.
    3) And based feels like matter.
    4) Then high energy takes less time to create change in your life?
    (1 vote)
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    • female robot ada style avatar for user Angelica Chen
      Analyze premise 1 again...
      Define elevated vs. Base. How can you categorize any given emotion, e.g. bittersweetness, pity, excitation. Also, explain the connection between emotion and "frequency". Frequency implies a wave form... Of what? Brain waves? Can you show that brain waves vary in frequency depending on emotion type? (I think not)

      Premise 2...
      What does energy feel like? How do you know?

      Premise 3...
      What does matter feel like? How is matter different different from energy objectively? Is this feeling truenfor every emotion? Is it more of a spectrum, or is it absolute? Does the feeling become modified depending on the emotion's intensity? Is there a way to have this feeling without the corresponding emotion? Are the feelings caused by the emotions, vice versa, or are they merely correlated?

      Premise 4...
      I don't even know how you got this from the rest of your premises...
      (2 votes)
  • aqualine ultimate style avatar for user Leo Karakolov
    P1) Leo identifies as a Rogue.
    P2) Leo enjoys playing games which have protagonists he can identify with.
    P3) Dishonored has a protagonist who is a rogue.
    C) Leo enjoys playing Dishonored.

    (1 vote)
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Video transcript

(intro music) Hi, I'm Aaron Ancell. I'm a graduate student at Duke University, and in this video I'm going to tell you about soundness, an important notion that philosophers use to evaluate arguments. Let's start by looking back at validity. You should already know what a valid argument is. If you don't, I encourage you to watch the video on validity before watching the rest of this video. As you learned in the video on validity, an argument is valid if it is impossible for all of the premises to be true while its conclusion is false. For example, the following is a valid argument. Premise (1): All cats are purple. Premise (2): Everything that is purple is a person. Conclusion: Therefore, all cats are people. This argument is valid, because it is impossible for the premises to be true while the conclusion is false. If all cats were purple, and all purple things were people, then all cats would be people. Of course, not all cats are purple, and not all purple things are people. So even though this argument is valid, it's not really informative. It does not establish the truth of its conclusion, since the premises are obviously false. Since the goal of an argument is usually to show that some conclusion is true, we usually want arguments that are more than just valid. This is where the notion of soundness comes in. Soundness is a technical notion in philosophy. What philosophers mean by "sound" is a bit different than what people ordinarily mean when they say things like "that was sound advice," or "she demonstrated sound judgement in making that decision." In philosophy, soundness, like validity, applies only to deductive arguments. In order to be sound, an argument must meet two requirements. First, the argument must be valid. All invalid arguments are unsound. Second, the premises of the argument must all be true. Any argument that has even a single false premise is unsound. To be sound, an argument must meet both requirements. Let's go back to the example with the purple cats. Is this argument sound? Let's check. The argument is valid, so it meets the first requirement. But it definitely does not meet the second requirement, since not all of its premises are true. In fact, both the premises are false. But not every unsound argument has false premises. Consider another example. Premise (1): All dead parrots are dead. Premise (2): Parrots are not frogs. Conclusion: Therefore, frogs exist. Both premises of this argument are true, so this argument satisfies the second requirement for being a sound argument. However, it doesn't satisfy the first requirement, because the argument is invalid. The conclusion does not follow from the premises. So this is an unsound argument, even though all the premises are true. Note that the conclusion is also true. But that doesn't matter. It's still an unsound argument. Here's another example. Premise (1): Ostriches cannot fly. Premise (2): All insects wear top hats. Conclusion: Therefore, ostriches are insects. This argument fails to meet both requirements. It isn't valid, and the second premise is false. So this argument is definitely unsound. "Now," you might ask, "why should I care "whether an argument is sound?" The reason is that if we know that an argument is sound, then we know that the conclusion of that argument must be true. There is no way that an argument can meet both requirements for soundness and have a false conclusion. To meet the first requirement, an argument must be valid. And by definition, a valid argument is one where the conclusion cannot be false if the premises are true. And to meet the second requirement, the premises of the argument must all be true. Putting the requirements for soundness together, we can say that a sound argument is one where the conclusion cannot be false if the premises are true, and where the premises are all true. This shows that the conclusion of a sound argument cannot be false. It has to be true. Sound arguments are very useful. They enable us to establish that things are true. Let's finish off by looking at an example. Premise (1): Whales do not have fur. Premise (2): Whales are mammals. Conclusion: Therefore, not all mammals have fur. This argument is valid. If the premises are true, then the conclusion must also be true. And the premises are true, so this is a sound argument, and the conclusion must be true. Give it a try. See if you can write a sound argument of your own. Subtitles by the Amara.org community