[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:04.44,0:00:10.46,Default,,0000,0000,0000,,Oh, hello. Welcome to the second unit of\Nour course. In the first unit, you learned
Dialogue: 0,0:00:10.46,0:00:16.55,Default,,0000,0000,0000,,how to listen to what someone was saying,\Nor read what they were writing, and find
Dialogue: 0,0:00:16.55,0:00:22.57,Default,,0000,0000,0000,,the argument in their words. You learned\Nwhat arguments are, what their parts are,
Dialogue: 0,0:00:22.57,0:00:28.30,Default,,0000,0000,0000,,and what they're used for. In this second\Nunit and the third unit that follows it,
Dialogue: 0,0:00:28.30,0:00:33.50,Default,,0000,0000,0000,,you're going to learn how to evaluate\Narguments. In the second unit, we're going
Dialogue: 0,0:00:33.09,0:00:38.50,Default,,0000,0000,0000,,to focus on deductive arguments. And in\Nthe third unit, you're going to focus on
Dialogue: 0,0:00:38.50,0:00:43.71,Default,,0000,0000,0000,,inductive arguments. So before we go any\Nfarther, I first need to explain the
Dialogue: 0,0:00:43.71,0:00:50.17,Default,,0000,0000,0000,,difference between deductive and inductive\Narguments. A deductive argument is an
Dialogue: 0,0:00:50.17,0:00:56.21,Default,,0000,0000,0000,,argument that's presented as being valid.\NNow, remember what it is for an argument
Dialogue: 0,0:00:56.21,0:01:02.10,Default,,0000,0000,0000,,to be valid. An argument is valid, just in\Ncase, there's no possible way for it's
Dialogue: 0,0:01:02.10,0:01:09.00,Default,,0000,0000,0000,,conclusion to be false, when all of it's\Npremises are true. See, I just got a new
Dialogue: 0,0:01:09.00,0:01:16.79,Default,,0000,0000,0000,,pet clown fish, Nimo. Now, maybe you don't\Nknow much about clown fish anatomy. But
Dialogue: 0,0:01:16.79,0:01:24.04,Default,,0000,0000,0000,,I'm going to try to persuade you right now\Nthat clown fish have gills. Here's an
Dialogue: 0,0:01:24.04,0:01:30.84,Default,,0000,0000,0000,,argument that I can give you for the\Nconclusion that clown fish have gills.
Dialogue: 0,0:01:30.84,0:01:38.09,Default,,0000,0000,0000,,Well, catfish have gills and goldfish have\Ngills, and sharks have gills. Therefore,
Dialogue: 0,0:01:38.09,0:01:45.64,Default,,0000,0000,0000,,clown fish have gills. Now, is that\Nargument valid? No, it's not. It's not
Dialogue: 0,0:01:45.64,0:01:52.47,Default,,0000,0000,0000,,valid because it's possible for the\Npremises to be true even when the
Dialogue: 0,0:01:52.47,0:02:00.08,Default,,0000,0000,0000,,conclusion is false. It could be that\Ncatfish, and sharks, and goldfish all have
Dialogue: 0,0:02:00.08,0:02:07.50,Default,,0000,0000,0000,,gills even though clownfish don't. But now\Nsuppose I give you a different argument,
Dialogue: 0,0:02:07.50,0:02:14.21,Default,,0000,0000,0000,,for the conclusion that clown fish have\Ngills. Here's how this different argument
Dialogue: 0,0:02:14.21,0:02:21.51,Default,,0000,0000,0000,,goes. All fish have gills, clown fish are\Na kind of fish. Therefore, clown fish have
Dialogue: 0,0:02:21.51,0:02:27.53,Default,,0000,0000,0000,,gills. Now, that argument is valid.\NThere's no possible way for the premises
Dialogue: 0,0:02:27.53,0:02:33.50,Default,,0000,0000,0000,,of that argument to be true if the\Nconclusion is false. I just gave you an
Dialogue: 0,0:02:33.50,0:02:39.06,Default,,0000,0000,0000,,example of a valid argument. But a valid\Nargument is not necessarily a deductive
Dialogue: 0,0:02:39.06,0:02:43.87,Default,,0000,0000,0000,,argument. And the deductive argument is\Nnot necessarily a valid argument. A
Dialogue: 0,0:02:43.87,0:02:48.74,Default,,0000,0000,0000,,deductive argument is an argument t hat's\Npresented as being valid. A deductive
Dialogue: 0,0:02:48.74,0:02:53.73,Default,,0000,0000,0000,,argument is successful only if it's valid.\NAnd in this second unit of the course,
Dialogue: 0,0:02:53.73,0:02:58.35,Default,,0000,0000,0000,,we're going to learn how to evaluate\Ndeductive arguments for validity. How to
Dialogue: 0,0:02:58.35,0:03:03.47,Default,,0000,0000,0000,,figure out whether or not they are valid.\NSo, I just gave an example of an argument
Dialogue: 0,0:03:03.47,0:03:08.59,Default,,0000,0000,0000,,and we figured out that it was valid. We\Nfigured out that it was valid by noticing
Dialogue: 0,0:03:08.59,0:03:13.52,Default,,0000,0000,0000,,that there was no possible way for the\Npremises to be true when the conclusion
Dialogue: 0,0:03:13.52,0:03:18.44,Default,,0000,0000,0000,,was false. So, if we could figure out\Nthat, that argument was valid, why do we
Dialogue: 0,0:03:18.44,0:03:23.74,Default,,0000,0000,0000,,need to do anything more for the second\Nunit of the course? It looks like we can
Dialogue: 0,0:03:23.74,0:03:29.17,Default,,0000,0000,0000,,just look at an argument and figure out\Nwhether or not it's valid. What's there to
Dialogue: 0,0:03:29.17,0:03:34.07,Default,,0000,0000,0000,,learn in this second unit? Well, what\Nwe're going to do in this second unit is
Dialogue: 0,0:03:34.07,0:03:39.36,Default,,0000,0000,0000,,learn some rules that we can use for\Nfiguring out when particular arguments are
Dialogue: 0,0:03:39.36,0:03:46.24,Default,,0000,0000,0000,,valid. Now, why are these rules good to\Nlearn? There are three reasons why it's
Dialogue: 0,0:03:46.24,0:03:51.83,Default,,0000,0000,0000,,good to learn these rules. The first\Nreason is that, sometimes using these
Dialogue: 0,0:03:51.83,0:03:57.96,Default,,0000,0000,0000,,rules can help you figure out whether a\Nparticular argument is valid. You see in
Dialogue: 0,0:03:57.96,0:04:04.02,Default,,0000,0000,0000,,some cases, it's not obvious just from\Nlooking at a particular argument that it
Dialogue: 0,0:04:04.02,0:04:12.80,Default,,0000,0000,0000,,is valid. Consider the following example.\NNo fish have wings. All birds have wings.
Dialogue: 0,0:04:12.80,0:04:20.94,Default,,0000,0000,0000,,All animals with gills are fish.\NTherefore, no birds have gills. Is that
Dialogue: 0,0:04:20.94,0:04:46.12,Default,,0000,0000,0000,,argument valid? Take a moment to think\Nabout it. It's not obvious is it? Well, if
Dialogue: 0,0:04:46.12,0:04:55.77,Default,,0000,0000,0000,,you knew the rules for evaluating\Narguments for validity, you'd be able to
Dialogue: 0,0:04:55.77,0:05:01.73,Default,,0000,0000,0000,,use those rules to figure out that, that\Nargument is valid. So, that's one reason
Dialogue: 0,0:05:01.73,0:05:05.74,Default,,0000,0000,0000,,why it's good to learn these rules.\NSometimes they help you to figure out
Dialogue: 0,0:05:05.74,0:05:10.14,Default,,0000,0000,0000,,whether a particular argument is valid.\NBut there's another reason why it's good
Dialogue: 0,0:05:10.14,0:05:14.15,Default,,0000,0000,0000,,to learn these rules. Even if they don't\Nhelp you to figure out whether a
Dialogue: 0,0:05:14.15,0:05:18.44,Default,,0000,0000,0000,,particular argument is valid, they can\Nhelp you to figure out why a particular
Dialogue: 0,0:05:18.44,0:05:25.32,Default,,0000,0000,0000,,argument is valid. So, in the example that\Nwe just considered about birds and fish,
Dialogue: 0,0:05:25.32,0:05:32.89,Default,,0000,0000,0000,,it turns out that there's a reason why\Nthat argument is valid. And the reason has
Dialogue: 0,0:05:32.89,0:05:40.83,Default,,0000,0000,0000,,to do wi th the meanings of the words, all\Nand know. Some of the rules that we'll
Dialogue: 0,0:05:40.83,0:05:47.15,Default,,0000,0000,0000,,learn for evaluating the validity of\Narguments, are rules that tell us the
Dialogue: 0,0:05:47.15,0:05:54.11,Default,,0000,0000,0000,,meanings of the words "all" and "no" as they\Noccur in that argument. And so those rules
Dialogue: 0,0:05:54.11,0:05:59.94,Default,,0000,0000,0000,,explain why the argument about the birds\Nand the fish is valid. And they explain it
Dialogue: 0,0:05:59.94,0:06:05.62,Default,,0000,0000,0000,,in terms of the meaning of the words "all"\Nand "no" that occur in that argument. So
Dialogue: 0,0:06:05.62,0:06:11.24,Default,,0000,0000,0000,,that's the second reason why it's good to\Nlearn these rules. Sometimes these rules
Dialogue: 0,0:06:11.24,0:06:16.73,Default,,0000,0000,0000,,help us to figure out why a particular\Nargument is valid. There's a third reason
Dialogue: 0,0:06:16.73,0:06:21.94,Default,,0000,0000,0000,,why it's good to learn these rules for\Nevaluating validity. And that is that,
Dialogue: 0,0:06:21.94,0:06:27.64,Default,,0000,0000,0000,,once we know these rules, evaluating the\Nvalidity of a deductive argument becomes a
Dialogue: 0,0:06:27.64,0:06:34.30,Default,,0000,0000,0000,,lot more fun. To illustrate, here's some\Npeople trying to evaluate the validity of
Dialogue: 0,0:06:34.30,0:06:42.32,Default,,0000,0000,0000,,deductive arguments without using these\Nrules. Now, here's some people trying to
Dialogue: 0,0:06:42.32,0:06:49.91,Default,,0000,0000,0000,,evaluate the validity of deductive\Narguments using these rules. See what I
Dialogue: 0,0:06:49.91,0:06:55.73,Default,,0000,0000,0000,,mean? The second group is obviously having\Nmore fun than the first. So, for those
Dialogue: 0,0:06:55.73,0:07:01.54,Default,,0000,0000,0000,,three reasons, it's good to learn these\Nrules. They can help you figure out when
Dialogue: 0,0:07:01.54,0:07:07.36,Default,,0000,0000,0000,,an argument is valid. They can help you\Nfigure out why an argument is valid. And,
Dialogue: 0,0:07:07.36,0:07:11.86,Default,,0000,0000,0000,,it can be a lot fun to use them. So now,\Ntime to learn the rules.