[Script Info]
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[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.07,0:00:05.83,Default,,0000,0000,0000,,(intro music)
Dialogue: 0,0:00:07.74,0:00:10.05,Default,,0000,0000,0000,,Hi, I'm Aaron Ancell.
Dialogue: 0,0:00:10.05,0:00:12.22,Default,,0000,0000,0000,,I'm a graduate student at Duke University,
Dialogue: 0,0:00:12.22,0:00:15.32,Default,,0000,0000,0000,,and in this video I'm going\Nto tell you about soundness,
Dialogue: 0,0:00:15.32,0:00:16.88,Default,,0000,0000,0000,,an important notion\Nthat philosophers use
Dialogue: 0,0:00:16.88,0:00:19.38,Default,,0000,0000,0000,,to evaluate arguments.
Dialogue: 0,0:00:19.38,0:00:21.74,Default,,0000,0000,0000,,Let's start by looking back at validity.
Dialogue: 0,0:00:21.74,0:00:24.22,Default,,0000,0000,0000,,You should already know\Nwhat a valid argument is.
Dialogue: 0,0:00:24.22,0:00:27.68,Default,,0000,0000,0000,,If you don't, I encourage you\Nto watch the video on validity
Dialogue: 0,0:00:27.68,0:00:31.47,Default,,0000,0000,0000,,before watching the rest of this video.
Dialogue: 0,0:00:31.47,0:00:33.66,Default,,0000,0000,0000,,As you learned in the video on validity,
Dialogue: 0,0:00:33.66,0:00:35.64,Default,,0000,0000,0000,,an argument is valid if it is impossible
Dialogue: 0,0:00:35.64,0:00:37.66,Default,,0000,0000,0000,,for all of the premises to be true
Dialogue: 0,0:00:37.66,0:00:39.68,Default,,0000,0000,0000,,while its conclusion is false.
Dialogue: 0,0:00:39.68,0:00:43.95,Default,,0000,0000,0000,,For example, the following\Nis a valid argument.
Dialogue: 0,0:00:43.95,0:00:47.64,Default,,0000,0000,0000,,Premise (1): All cats are purple.
Dialogue: 0,0:00:47.64,0:00:52.64,Default,,0000,0000,0000,,Premise (2): Everything\Nthat is purple is a person.
Dialogue: 0,0:00:52.75,0:00:56.86,Default,,0000,0000,0000,,Conclusion: Therefore,\Nall cats are people.
Dialogue: 0,0:00:57.86,0:01:00.16,Default,,0000,0000,0000,,This argument is valid,\Nbecause it is impossible
Dialogue: 0,0:01:00.16,0:01:04.15,Default,,0000,0000,0000,,for the premises to be true\Nwhile the conclusion is false.
Dialogue: 0,0:01:04.15,0:01:08.67,Default,,0000,0000,0000,,If all cats were purple, and\Nall purple things were people,
Dialogue: 0,0:01:08.67,0:01:11.64,Default,,0000,0000,0000,,then all cats would be people.
Dialogue: 0,0:01:11.64,0:01:14.15,Default,,0000,0000,0000,,Of course, not all cats are purple,
Dialogue: 0,0:01:14.15,0:01:16.21,Default,,0000,0000,0000,,and not all purple things are people.
Dialogue: 0,0:01:16.21,0:01:18.26,Default,,0000,0000,0000,,So even though this argument is valid,
Dialogue: 0,0:01:18.26,0:01:20.33,Default,,0000,0000,0000,,it's not really informative.
Dialogue: 0,0:01:20.33,0:01:22.77,Default,,0000,0000,0000,,It does not establish the\Ntruth of its conclusion,
Dialogue: 0,0:01:22.77,0:01:25.41,Default,,0000,0000,0000,,since the premises are obviously false.
Dialogue: 0,0:01:26.28,0:01:28.43,Default,,0000,0000,0000,,Since the goal of an\Nargument is usually to show
Dialogue: 0,0:01:28.43,0:01:31.24,Default,,0000,0000,0000,,that some conclusion is true,
Dialogue: 0,0:01:31.24,0:01:34.65,Default,,0000,0000,0000,,we usually want arguments\Nthat are more than just valid.
Dialogue: 0,0:01:34.91,0:01:38.03,Default,,0000,0000,0000,,This is where the notion\Nof soundness comes in.
Dialogue: 0,0:01:38.38,0:01:41.88,Default,,0000,0000,0000,,Soundness is a technical\Nnotion in philosophy.
Dialogue: 0,0:01:41.88,0:01:44.23,Default,,0000,0000,0000,,What philosophers mean by "sound"
Dialogue: 0,0:01:44.23,0:01:47.34,Default,,0000,0000,0000,,is a bit different than\Nwhat people ordinarily mean
Dialogue: 0,0:01:47.34,0:01:50.44,Default,,0000,0000,0000,,when they say things like\N"that was sound advice,"
Dialogue: 0,0:01:50.44,0:01:52.90,Default,,0000,0000,0000,,or "she demonstrated sound judgement
Dialogue: 0,0:01:52.90,0:01:55.49,Default,,0000,0000,0000,,in making that decision."
Dialogue: 0,0:01:55.49,0:01:58.48,Default,,0000,0000,0000,,In philosophy, soundness, like validity,
Dialogue: 0,0:01:58.48,0:02:00.91,Default,,0000,0000,0000,,applies only to deductive arguments.
Dialogue: 0,0:02:00.91,0:02:02.88,Default,,0000,0000,0000,,In order to be sound, an argument
Dialogue: 0,0:02:02.88,0:02:04.93,Default,,0000,0000,0000,,must meet two requirements.
Dialogue: 0,0:02:04.93,0:02:08.11,Default,,0000,0000,0000,,First, the argument must be valid.
Dialogue: 0,0:02:08.11,0:02:11.57,Default,,0000,0000,0000,,All invalid arguments are unsound.
Dialogue: 0,0:02:11.57,0:02:15.65,Default,,0000,0000,0000,,Second, the premises of the\Nargument must all be true.
Dialogue: 0,0:02:15.65,0:02:18.41,Default,,0000,0000,0000,,Any argument that has even\Na single false premise
Dialogue: 0,0:02:18.41,0:02:20.37,Default,,0000,0000,0000,,is unsound.
Dialogue: 0,0:02:20.37,0:02:23.82,Default,,0000,0000,0000,,To be sound, an argument\Nmust meet both requirements.
Dialogue: 0,0:02:23.82,0:02:27.10,Default,,0000,0000,0000,,Let's go back to the example\Nwith the purple cats.
Dialogue: 0,0:02:27.10,0:02:30.50,Default,,0000,0000,0000,,Is this argument sound? Let's check.
Dialogue: 0,0:02:30.50,0:02:33.74,Default,,0000,0000,0000,,The argument is valid, so it\Nmeets the first requirement.
Dialogue: 0,0:02:33.74,0:02:36.36,Default,,0000,0000,0000,,But it definitely does not\Nmeet the second requirement,
Dialogue: 0,0:02:36.36,0:02:38.55,Default,,0000,0000,0000,,since not all of its premises are true.
Dialogue: 0,0:02:38.55,0:02:41.93,Default,,0000,0000,0000,,In fact, both the premises are false.
Dialogue: 0,0:02:41.93,0:02:44.97,Default,,0000,0000,0000,,But not every unsound\Nargument has false premises.
Dialogue: 0,0:02:44.97,0:02:46.76,Default,,0000,0000,0000,,Consider another example.
Dialogue: 0,0:02:46.76,0:02:50.67,Default,,0000,0000,0000,,Premise (1): All dead parrots are dead.
Dialogue: 0,0:02:50.67,0:02:54.55,Default,,0000,0000,0000,,Premise (2): Parrots are not frogs.
Dialogue: 0,0:02:54.55,0:02:58.88,Default,,0000,0000,0000,,Conclusion: Therefore, frogs exist.
Dialogue: 0,0:02:58.88,0:03:00.96,Default,,0000,0000,0000,,Both premises of this argument are true,
Dialogue: 0,0:03:00.96,0:03:03.20,Default,,0000,0000,0000,,so this argument satisfies\Nthe second requirement
Dialogue: 0,0:03:03.20,0:03:04.79,Default,,0000,0000,0000,,for being a sound argument.
Dialogue: 0,0:03:04.79,0:03:07.54,Default,,0000,0000,0000,,However, it doesn't satisfy\Nthe first requirement,
Dialogue: 0,0:03:07.54,0:03:10.10,Default,,0000,0000,0000,,because the argument is invalid.
Dialogue: 0,0:03:10.10,0:03:12.48,Default,,0000,0000,0000,,The conclusion does not\Nfollow from the premises.
Dialogue: 0,0:03:12.48,0:03:14.20,Default,,0000,0000,0000,,So this is an unsound argument,
Dialogue: 0,0:03:14.20,0:03:16.61,Default,,0000,0000,0000,,even though all the premises are true.
Dialogue: 0,0:03:16.61,0:03:18.66,Default,,0000,0000,0000,,Note that the conclusion is also true.
Dialogue: 0,0:03:18.66,0:03:19.66,Default,,0000,0000,0000,,But that doesn't matter.
Dialogue: 0,0:03:19.66,0:03:22.45,Default,,0000,0000,0000,,It's still an unsound argument.
Dialogue: 0,0:03:22.45,0:03:24.25,Default,,0000,0000,0000,,Here's another example.
Dialogue: 0,0:03:24.25,0:03:27.79,Default,,0000,0000,0000,,Premise (1): Ostriches cannot fly.
Dialogue: 0,0:03:27.79,0:03:32.14,Default,,0000,0000,0000,,Premise (2): All insects wear top hats.
Dialogue: 0,0:03:32.14,0:03:36.48,Default,,0000,0000,0000,,Conclusion: Therefore,\Nostriches are insects.
Dialogue: 0,0:03:36.48,0:03:39.06,Default,,0000,0000,0000,,This argument fails to\Nmeet both requirements.
Dialogue: 0,0:03:39.06,0:03:42.16,Default,,0000,0000,0000,,It isn't valid, and the\Nsecond premise is false.
Dialogue: 0,0:03:42.16,0:03:45.17,Default,,0000,0000,0000,,So this argument is definitely unsound.
Dialogue: 0,0:03:45.17,0:03:47.49,Default,,0000,0000,0000,,"Now," you might ask, "why should I care
Dialogue: 0,0:03:47.49,0:03:49.43,Default,,0000,0000,0000,,"whether an argument is sound?"
Dialogue: 0,0:03:49.43,0:03:52.32,Default,,0000,0000,0000,,The reason is that if we know\Nthat an argument is sound,
Dialogue: 0,0:03:52.32,0:03:54.47,Default,,0000,0000,0000,,then we know that the\Nconclusion of that argument
Dialogue: 0,0:03:54.47,0:03:56.10,Default,,0000,0000,0000,,must be true.
Dialogue: 0,0:03:56.10,0:03:57.85,Default,,0000,0000,0000,,There is no way that an argument can meet
Dialogue: 0,0:03:57.85,0:03:59.81,Default,,0000,0000,0000,,both requirements for soundness
Dialogue: 0,0:03:59.81,0:04:01.96,Default,,0000,0000,0000,,and have a false conclusion.
Dialogue: 0,0:04:01.96,0:04:03.57,Default,,0000,0000,0000,,To meet the first requirement,
Dialogue: 0,0:04:03.57,0:04:05.26,Default,,0000,0000,0000,,an argument must be valid.
Dialogue: 0,0:04:05.26,0:04:07.45,Default,,0000,0000,0000,,And by definition, a valid argument
Dialogue: 0,0:04:07.45,0:04:09.85,Default,,0000,0000,0000,,is one where the\Nconclusion cannot be false
Dialogue: 0,0:04:09.85,0:04:12.21,Default,,0000,0000,0000,,if the premises are true.
Dialogue: 0,0:04:12.21,0:04:13.97,Default,,0000,0000,0000,,And to meet the second requirement,
Dialogue: 0,0:04:13.97,0:04:17.27,Default,,0000,0000,0000,,the premises of the\Nargument must all be true.
Dialogue: 0,0:04:17.27,0:04:19.71,Default,,0000,0000,0000,,Putting the requirements\Nfor soundness together,
Dialogue: 0,0:04:19.71,0:04:21.53,Default,,0000,0000,0000,,we can say that a sound argument
Dialogue: 0,0:04:21.53,0:04:24.02,Default,,0000,0000,0000,,is one where the\Nconclusion cannot be false
Dialogue: 0,0:04:24.02,0:04:25.77,Default,,0000,0000,0000,,if the premises are true,
Dialogue: 0,0:04:25.77,0:04:28.07,Default,,0000,0000,0000,,and where the premises are all true.
Dialogue: 0,0:04:28.07,0:04:31.57,Default,,0000,0000,0000,,This shows that the conclusion of\Na sound argument cannot be false.
Dialogue: 0,0:04:31.57,0:04:33.21,Default,,0000,0000,0000,,It has to be true.
Dialogue: 0,0:04:33.69,0:04:35.92,Default,,0000,0000,0000,,Sound arguments are very useful.
Dialogue: 0,0:04:35.92,0:04:38.86,Default,,0000,0000,0000,,They enable us to establish\Nthat things are true.
Dialogue: 0,0:04:38.86,0:04:41.43,Default,,0000,0000,0000,,Let's finish off by looking at an example.
Dialogue: 0,0:04:41.43,0:04:44.81,Default,,0000,0000,0000,,Premise (1): Whales do not have fur.
Dialogue: 0,0:04:44.81,0:04:47.83,Default,,0000,0000,0000,,Premise (2): Whales are mammals.
Dialogue: 0,0:04:47.83,0:04:51.58,Default,,0000,0000,0000,,Conclusion: Therefore,\Nnot all mammals have fur.
Dialogue: 0,0:04:52.68,0:04:54.41,Default,,0000,0000,0000,,This argument is valid.
Dialogue: 0,0:04:54.41,0:04:55.93,Default,,0000,0000,0000,,If the premises are true,
Dialogue: 0,0:04:55.93,0:04:58.34,Default,,0000,0000,0000,,then the conclusion must also be true.
Dialogue: 0,0:04:58.34,0:05:01.68,Default,,0000,0000,0000,,And the premises are true,\Nso this is a sound argument,
Dialogue: 0,0:05:01.68,0:05:03.83,Default,,0000,0000,0000,,and the conclusion must be true.
Dialogue: 0,0:05:03.83,0:05:05.34,Default,,0000,0000,0000,,Give it a try.
Dialogue: 0,0:05:05.34,0:05:08.31,Default,,0000,0000,0000,,See if you can write a\Nsound argument of your own.