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Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.07,0:00:03.91,Default,,0000,0000,0000,,[Music]
Dialogue: 0,0:00:03.91,0:00:07.45,Default,,0000,0000,0000,,Scientists often gather data through
Dialogue: 0,0:00:07.45,0:00:10.96,Default,,0000,0000,0000,,observation experiments, archival studies
Dialogue: 0,0:00:10.96,0:00:14.31,Default,,0000,0000,0000,,and so on. But they are rarely satisfied
Dialogue: 0,0:00:14.31,0:00:17.53,Default,,0000,0000,0000,,with data alone. Scientists want to draw
Dialogue: 0,0:00:17.53,0:00:20.06,Default,,0000,0000,0000,,conclusions from those data. They want to
Dialogue: 0,0:00:20.06,0:00:21.97,Default,,0000,0000,0000,,use the data to show that certain
Dialogue: 0,0:00:21.97,0:00:24.59,Default,,0000,0000,0000,,theories are right and others are wrong.
Dialogue: 0,0:00:25.30,0:00:27.86,Default,,0000,0000,0000,,To understand science, then, it will be
Dialogue: 0,0:00:27.86,0:00:29.68,Default,,0000,0000,0000,,important to understand when it is
Dialogue: 0,0:00:29.68,0:00:31.85,Default,,0000,0000,0000,,legitimate and when it is illegitimate
Dialogue: 0,0:00:31.85,0:00:35.32,Default,,0000,0000,0000,,to draw a specific conclusion from what
Dialogue: 0,0:00:35.32,0:00:37.39,Default,,0000,0000,0000,,we already know. We need to understand
Dialogue: 0,0:00:37.39,0:00:42.66,Default,,0000,0000,0000,,arguments; and that is why, in this
Dialogue: 0,0:00:37.39,0:00:40.03,Default,,0000,0000,0000,,the difference between good and bad
Dialogue: 0,0:00:43.34,0:00:45.36,Default,,0000,0000,0000,,lecture, we will take a look at logic--the
Dialogue: 0,0:00:45.36,0:00:49.45,Default,,0000,0000,0000,,study of argumentation. Let us first
Dialogue: 0,0:00:49.45,0:00:53.30,Default,,0000,0000,0000,,introduce some terminology. An argument
Dialogue: 0,0:00:53.30,0:00:56.15,Default,,0000,0000,0000,,consists of two parts: the premises and
Dialogue: 0,0:00:56.15,0:00:59.39,Default,,0000,0000,0000,,the conclusion. The premises are the
Dialogue: 0,0:00:59.39,0:01:02.18,Default,,0000,0000,0000,,things we presuppose and the conclusion
Dialogue: 0,0:01:02.18,0:01:06.28,Default,,0000,0000,0000,,is what we conclude from those premises.
Dialogue: 0,0:01:06.28,0:01:08.45,Default,,0000,0000,0000,,So let's look at an example:
Dialogue: 0,0:01:08.45,0:01:12.22,Default,,0000,0000,0000,,No medieval King had absolute power over
Dialogue: 0,0:01:12.22,0:01:15.99,Default,,0000,0000,0000,,his subjects. Louis 7 of France was a
Dialogue: 0,0:01:15.99,0:01:20.66,Default,,0000,0000,0000,,medieval King. So Louis 7 of France did
Dialogue: 0,0:01:20.66,0:01:23.07,Default,,0000,0000,0000,,not have absolute power over his
Dialogue: 0,0:01:23.07,0:01:26.52,Default,,0000,0000,0000,,subjects. Here the first two lines are
Dialogue: 0,0:01:26.52,0:01:29.55,Default,,0000,0000,0000,,the premises and a final line introduced
Dialogue: 0,0:01:29.55,0:01:33.42,Default,,0000,0000,0000,,by the word "so" is the conclusion. In this
Dialogue: 0,0:01:33.42,0:01:35.66,Default,,0000,0000,0000,,argument we assume that medieval kings
Dialogue: 0,0:01:35.66,0:01:38.12,Default,,0000,0000,0000,,did not have absolute power and that
Dialogue: 0,0:01:38.12,0:01:40.72,Default,,0000,0000,0000,,Louis 7 was a medieval King. And we
Dialogue: 0,0:01:40.72,0:01:43.18,Default,,0000,0000,0000,,conclude that he did not have absolute
Dialogue: 0,0:01:43.18,0:01:47.31,Default,,0000,0000,0000,,power. As a second piece of terminology
Dialogue: 0,0:01:47.31,0:01:50.04,Default,,0000,0000,0000,,we will make a distinction between valid
Dialogue: 0,0:01:50.04,0:01:53.51,Default,,0000,0000,0000,,and invalid arguments. A valid argument
Dialogue: 0,0:01:53.51,0:01:55.61,Default,,0000,0000,0000,,is an argument in which the conclusion
Dialogue: 0,0:01:55.61,0:01:58.45,Default,,0000,0000,0000,,really follows from the premises.
Dialogue: 0,0:01:58.45,0:02:01.62,Default,,0000,0000,0000,,Our example about Louis 7 is an example
Dialogue: 0,0:02:01.62,0:02:04.31,Default,,0000,0000,0000,,of a valid argument. The conclusion
Dialogue: 0,0:02:04.31,0:02:07.34,Default,,0000,0000,0000,,really follows from the premises. It
Dialogue: 0,0:02:07.34,0:02:10.38,Default,,0000,0000,0000,,makes sense to draw this conclusion from
Dialogue: 0,0:02:10.38,0:02:12.72,Default,,0000,0000,0000,,these premises.
Dialogue: 0,0:02:12.72,0:02:15.89,Default,,0000,0000,0000,,As an example of an invalid argument we
Dialogue: 0,0:02:15.89,0:02:18.98,Default,,0000,0000,0000,,can take this: No medieval King had
Dialogue: 0,0:02:18.98,0:02:22.39,Default,,0000,0000,0000,,absolute power over his subjects. Louis
Dialogue: 0,0:02:22.39,0:02:25.08,Default,,0000,0000,0000,,seven of France was a great horseman. So
Dialogue: 0,0:02:25.08,0:02:27.87,Default,,0000,0000,0000,,Louis seven of France did not have
Dialogue: 0,0:02:27.87,0:02:31.90,Default,,0000,0000,0000,,absolute power over his subjects. We just
Dialogue: 0,0:02:31.90,0:02:34.47,Default,,0000,0000,0000,,can't draw that conclusion from those
Dialogue: 0,0:02:34.47,0:02:37.53,Default,,0000,0000,0000,,premises. So this argument is not valid.
Dialogue: 0,0:02:37.53,0:02:41.20,Default,,0000,0000,0000,,It's invalid. Note that whether an
Dialogue: 0,0:02:41.20,0:02:42.47,Default,,0000,0000,0000,,argument is valid or not
Dialogue: 0,0:02:42.47,0:02:44.05,Default,,0000,0000,0000,,has nothing to do with whether the
Dialogue: 0,0:02:44.05,0:02:46.68,Default,,0000,0000,0000,,premises or the conclusions are true.
Dialogue: 0,0:02:46.68,0:02:49.68,Default,,0000,0000,0000,,Perhaps Louis 7 really was a great
Dialogue: 0,0:02:49.68,0:02:52.17,Default,,0000,0000,0000,,horseman. Then all the premises and the
Dialogue: 0,0:02:52.17,0:02:54.38,Default,,0000,0000,0000,,conclusion of that argument are true and
Dialogue: 0,0:02:54.38,0:02:58.03,Default,,0000,0000,0000,,yet the argument is invalid because the
Dialogue: 0,0:02:58.03,0:03:01.12,Default,,0000,0000,0000,,conclusion just doesn't follow from the
Dialogue: 0,0:03:01.12,0:03:04.30,Default,,0000,0000,0000,,premises. On the other hand it's also
Dialogue: 0,0:03:04.30,0:03:06.78,Default,,0000,0000,0000,,possible to have false premises and a
Dialogue: 0,0:03:06.78,0:03:10.60,Default,,0000,0000,0000,,valid argument. For instance: No medieval
Dialogue: 0,0:03:10.60,0:03:12.18,Default,,0000,0000,0000,,King had absolute power over his
Dialogue: 0,0:03:12.18,0:03:14.72,Default,,0000,0000,0000,,subjects. Victor Gijsbers was a
Dialogue: 0,0:03:14.72,0:03:17.83,Default,,0000,0000,0000,,medieval king. So Victor Gijsbers did not
Dialogue: 0,0:03:17.83,0:03:20.37,Default,,0000,0000,0000,,have absolute power over his subjects.
Dialogue: 0,0:03:20.37,0:03:24.15,Default,,0000,0000,0000,,This argument is perfectly valid even
Dialogue: 0,0:03:24.15,0:03:25.61,Default,,0000,0000,0000,,though the assumption that I am a
Dialogue: 0,0:03:25.61,0:03:28.43,Default,,0000,0000,0000,,medieval King is, as far as I know, false.
Dialogue: 0,0:03:28.43,0:03:29.75,Default,,0000,0000,0000,,We can now introduce our final piece of
Dialogue: 0,0:03:29.75,0:03:35.11,Default,,0000,0000,0000,,terminology: The distinction between two
Dialogue: 0,0:03:35.61,0:03:38.74,Default,,0000,0000,0000,,kinds of arguments. Deductive arguments
Dialogue: 0,0:03:38.74,0:03:42.20,Default,,0000,0000,0000,,and inductive arguments. A deductive
Dialogue: 0,0:03:42.23,0:03:44.34,Default,,0000,0000,0000,,argument is an argument in which the
Dialogue: 0,0:03:44.34,0:03:46.25,Default,,0000,0000,0000,,truth of the premises
Dialogue: 0,0:03:46.27,0:03:49.26,Default,,0000,0000,0000,,absolutely guarantee the truth of the
Dialogue: 0,0:03:49.26,0:03:52.48,Default,,0000,0000,0000,,conclusion. It's just not possible for
Dialogue: 0,0:03:52.48,0:03:54.45,Default,,0000,0000,0000,,the premises to be true and the
Dialogue: 0,0:03:54.45,0:03:56.85,Default,,0000,0000,0000,,conclusion to be false.
Dialogue: 0,0:03:56.85,0:03:59.44,Default,,0000,0000,0000,,Returning to our original example, we can
Dialogue: 0,0:03:59.44,0:04:01.78,Default,,0000,0000,0000,,see that this is a deductive argument. It
Dialogue: 0,0:04:01.78,0:04:03.12,Default,,0000,0000,0000,,is true
Dialogue: 0,0:04:03.12,0:04:04.94,Default,,0000,0000,0000,,the medieval Kings did not have absolute
Dialogue: 0,0:04:04.94,0:04:07.51,Default,,0000,0000,0000,,power; and if it is true that Louis 7 was
Dialogue: 0,0:04:07.51,0:04:10.58,Default,,0000,0000,0000,,a medieval King, then it must be true
Dialogue: 0,0:04:10.58,0:04:13.19,Default,,0000,0000,0000,,that he did not have absolute power.
Dialogue: 0,0:04:13.19,0:04:15.57,Default,,0000,0000,0000,,Or, in other words, if he did have
Dialogue: 0,0:04:15.57,0:04:17.99,Default,,0000,0000,0000,,absolute power then one of those two
Dialogue: 0,0:04:17.99,0:04:22.63,Default,,0000,0000,0000,,premises must be wrong. I'll come to the
Dialogue: 0,0:04:22.63,0:04:24.47,Default,,0000,0000,0000,,definition of inductive arguments in a
Dialogue: 0,0:04:24.47,0:04:27.05,Default,,0000,0000,0000,,moment, but first I want to point out two
Dialogue: 0,0:04:27.05,0:04:28.96,Default,,0000,0000,0000,,interesting features of deductive
Dialogue: 0,0:04:28.96,0:04:33.08,Default,,0000,0000,0000,,arguments: First, if you use deductive
Dialogue: 0,0:04:33.08,0:04:36.47,Default,,0000,0000,0000,,arguments you can't make any new
Dialogue: 0,0:04:36.47,0:04:40.07,Default,,0000,0000,0000,,mistakes. The only way for the conclusion
Dialogue: 0,0:04:40.07,0:04:42.21,Default,,0000,0000,0000,,of a deductive argument to be false is
Dialogue: 0,0:04:42.21,0:04:45.71,Default,,0000,0000,0000,,if one of your assumptions is false, so
Dialogue: 0,0:04:45.71,0:04:47.94,Default,,0000,0000,0000,,if you already believe something false
Dialogue: 0,0:04:47.94,0:04:50.28,Default,,0000,0000,0000,,then your conclusion may end up being
Dialogue: 0,0:04:50.28,0:04:52.93,Default,,0000,0000,0000,,false. But if your assumptions are true
Dialogue: 0,0:04:52.93,0:04:56.58,Default,,0000,0000,0000,,your conclusions are guaranteed to be
Dialogue: 0,0:04:56.58,0:04:57.54,Default,,0000,0000,0000,,true as well.
Dialogue: 0,0:04:57.54,0:05:00.87,Default,,0000,0000,0000,,So deductive arguments never introduce
Dialogue: 0,0:05:00.87,0:05:03.57,Default,,0000,0000,0000,,falsehoods if they weren't already there.
Dialogue: 0,0:05:03.57,0:05:06.05,Default,,0000,0000,0000,,And that makes them very strong and good
Dialogue: 0,0:05:06.05,0:05:08.23,Default,,0000,0000,0000,,arguments to use, because they're not
Dialogue: 0,0:05:08.23,0:05:13.29,Default,,0000,0000,0000,,very risky. Second, logicians found out
Dialogue: 0,0:05:13.29,0:05:16.12,Default,,0000,0000,0000,,already more than 2,000 years ago--and
Dialogue: 0,0:05:16.12,0:05:18.15,Default,,0000,0000,0000,,Aristotle played an important role here--
Dialogue: 0,0:05:18.15,0:05:20.85,Default,,0000,0000,0000,,that whether a deductive argument is
Dialogue: 0,0:05:20.85,0:05:23.76,Default,,0000,0000,0000,,valid or not can be determined just by
Dialogue: 0,0:05:23.76,0:05:26.08,Default,,0000,0000,0000,,looking at the form of the argument and
Dialogue: 0,0:05:26.08,0:05:29.44,Default,,0000,0000,0000,,ignoring its content. Even if you know
Dialogue: 0,0:05:29.44,0:05:32.58,Default,,0000,0000,0000,,nothing about medieval kings and Louis 7
Dialogue: 0,0:05:32.58,0:05:35.41,Default,,0000,0000,0000,,you can still see that our example
Dialogue: 0,0:05:35.41,0:05:39.31,Default,,0000,0000,0000,,argument is valid. How? Because there's
Dialogue: 0,0:05:39.31,0:05:44.47,Default,,0000,0000,0000,,this form: No A is B. C is A. So C is not B.
Dialogue: 0,0:05:44.47,0:05:47.89,Default,,0000,0000,0000,,Where A is "medieval King," B is "someone
Dialogue: 0,0:05:47.89,0:05:51.49,Default,,0000,0000,0000,,with absolute power," and C is "Louis 7" But
Dialogue: 0,0:05:51.49,0:05:53.66,Default,,0000,0000,0000,,we can put anything we like in the place
Dialogue: 0,0:05:53.66,0:05:55.46,Default,,0000,0000,0000,,of those letters and the argument will
Dialogue: 0,0:05:55.46,0:05:58.49,Default,,0000,0000,0000,,remain valid. For instance, let's choose A
Dialogue: 0,0:05:58.49,0:06:02.04,Default,,0000,0000,0000,,"Is a Dutchman" B "is humble" and C "is Victor
Dialogue: 0,0:06:02.04,0:06:05.18,Default,,0000,0000,0000,,or Gijsbers" Then we have: No Dutchman
Dialogue: 0,0:06:05.18,0:06:07.24,Default,,0000,0000,0000,,is humble. Victor Gijsbers is a
Dialogue: 0,0:06:07.24,0:06:10.01,Default,,0000,0000,0000,,Dutchman. So Victor Gijsbers is not
Dialogue: 0,0:06:10.01,0:06:12.80,Default,,0000,0000,0000,,humble. Which is another valid argument.
Dialogue: 0,0:06:12.80,0:06:15.21,Default,,0000,0000,0000,,Although of course the first premise is
Dialogue: 0,0:06:15.21,0:06:18.67,Default,,0000,0000,0000,,false and so is the conclusion. So we can
Dialogue: 0,0:06:18.67,0:06:20.56,Default,,0000,0000,0000,,see whether a deductive argument is
Dialogue: 0,0:06:20.56,0:06:22.79,Default,,0000,0000,0000,,valid simply by looking at its form
Dialogue: 0,0:06:22.79,0:06:24.85,Default,,0000,0000,0000,,without knowing anything about its
Dialogue: 0,0:06:24.85,0:06:27.77,Default,,0000,0000,0000,,content. And that is really important
Dialogue: 0,0:06:27.77,0:06:30.00,Default,,0000,0000,0000,,because that means that we can see
Dialogue: 0,0:06:30.00,0:06:31.88,Default,,0000,0000,0000,,whether something is a good argument
Dialogue: 0,0:06:31.88,0:06:35.34,Default,,0000,0000,0000,,without making any prior theoretical
Dialogue: 0,0:06:35.34,0:06:38.13,Default,,0000,0000,0000,,assumptions about the content matter. If
Dialogue: 0,0:06:38.13,0:06:40.86,Default,,0000,0000,0000,,we believe that scientists first
Dialogue: 0,0:06:40.86,0:06:42.86,Default,,0000,0000,0000,,collect data and then come to a
Dialogue: 0,0:06:42.86,0:06:44.55,Default,,0000,0000,0000,,conclusion about which theories are
Dialogue: 0,0:06:44.55,0:06:47.26,Default,,0000,0000,0000,,right and wrong, this is exactly what we
Dialogue: 0,0:06:47.26,0:06:50.53,Default,,0000,0000,0000,,would expect. We only need the data and
Dialogue: 0,0:06:50.53,0:06:53.26,Default,,0000,0000,0000,,some valid arguments which can be shown
Dialogue: 0,0:06:53.26,0:06:56.15,Default,,0000,0000,0000,,to be valid independent of any theories
Dialogue: 0,0:06:56.15,0:06:58.75,Default,,0000,0000,0000,,or ideas, and then we draw our
Dialogue: 0,0:06:58.75,0:07:02.58,Default,,0000,0000,0000,,conclusions. It would be great if science
Dialogue: 0,0:07:02.58,0:07:08.02,Default,,0000,0000,0000,,worked like that. Unfortunately, and I bet
Dialogue: 0,0:07:08.02,0:07:09.55,Default,,0000,0000,0000,,you saw that coming,
Dialogue: 0,0:07:09.55,0:07:13.21,Default,,0000,0000,0000,,science doesn't work like that. And it
Dialogue: 0,0:07:13.21,0:07:14.75,Default,,0000,0000,0000,,doesn't work like that because the most
Dialogue: 0,0:07:14.75,0:07:17.29,Default,,0000,0000,0000,,important arguments in science are not
Dialogue: 0,0:07:17.29,0:07:21.93,Default,,0000,0000,0000,,deductive. They are inductive. Remember
Dialogue: 0,0:07:21.93,0:07:23.86,Default,,0000,0000,0000,,that a deductive argument is an argument
Dialogue: 0,0:07:23.86,0:07:26.37,Default,,0000,0000,0000,,such that the truth of the premises
Dialogue: 0,0:07:26.37,0:07:29.05,Default,,0000,0000,0000,,absolutely guarantees the truth of the
Dialogue: 0,0:07:29.05,0:07:33.12,Default,,0000,0000,0000,,conclusion. An inductive argument is an
Dialogue: 0,0:07:33.12,0:07:34.66,Default,,0000,0000,0000,,argument where the truth of the premises
Dialogue: 0,0:07:34.66,0:07:36.63,Default,,0000,0000,0000,,gives good reason to believe the
Dialogue: 0,0:07:36.63,0:07:39.69,Default,,0000,0000,0000,,conclusion but does not absolutely
Dialogue: 0,0:07:39.69,0:07:43.56,Default,,0000,0000,0000,,guarantee its truth. Again let's look at
Dialogue: 0,0:07:43.56,0:07:44.26,Default,,0000,0000,0000,,an example:
Dialogue: 0,0:07:44.26,0:07:46.82,Default,,0000,0000,0000,,None of the medieval texts we have
Dialogue: 0,0:07:46.82,0:07:49.13,Default,,0000,0000,0000,,studied argues against the existence of
Dialogue: 0,0:07:49.13,0:07:52.75,Default,,0000,0000,0000,,God, so no scholar in the Middle Ages
Dialogue: 0,0:07:52.75,0:07:55.60,Default,,0000,0000,0000,,argued against the existence of God.
Dialogue: 0,0:07:55.60,0:07:58.75,Default,,0000,0000,0000,,That's a valid argument if it's true
Dialogue: 0,0:07:58.75,0:08:00.60,Default,,0000,0000,0000,,that none of the texts we have makes
Dialogue: 0,0:08:00.60,0:08:03.10,Default,,0000,0000,0000,,this argument, and we have a lot of texts,
Dialogue: 0,0:08:03.10,0:08:05.88,Default,,0000,0000,0000,,and it's quite plausible that nobody in
Dialogue: 0,0:08:05.88,0:08:08.20,Default,,0000,0000,0000,,that time actually made this argument.
Dialogue: 0,0:08:08.20,0:08:12.37,Default,,0000,0000,0000,,But it's indeed only plausible. It could
Dialogue: 0,0:08:12.37,0:08:14.58,Default,,0000,0000,0000,,be that the argument was made but
Dialogue: 0,0:08:14.58,0:08:18.43,Default,,0000,0000,0000,,somehow it wasn't transmitted to us. So
Dialogue: 0,0:08:18.43,0:08:20.94,Default,,0000,0000,0000,,in an inductive argument. The truth of
Dialogue: 0,0:08:20.94,0:08:23.07,Default,,0000,0000,0000,,the premises makes the conclusion likely,
Dialogue: 0,0:08:23.07,0:08:26.56,Default,,0000,0000,0000,,but it doesn't guarantee it. And that's
Dialogue: 0,0:08:26.56,0:08:29.20,Default,,0000,0000,0000,,generally the case in science. We have
Dialogue: 0,0:08:29.20,0:08:31.49,Default,,0000,0000,0000,,some limited data. We want to draw a
Dialogue: 0,0:08:31.49,0:08:34.08,Default,,0000,0000,0000,,general conclusion from those, and our
Dialogue: 0,0:08:34.08,0:08:36.42,Default,,0000,0000,0000,,data makes the conclusion likely but
Dialogue: 0,0:08:36.42,0:08:41.79,Default,,0000,0000,0000,,they don't make it certain. So, in science,
Dialogue: 0,0:08:36.45,0:08:41.79,Default,,0000,0000,0000,,we are continually making inductive
Dialogue: 0,0:08:41.79,0:08:44.69,Default,,0000,0000,0000,,arguments. And, as we will see in the next
Dialogue: 0,0:08:44.69,0:08:48.21,Default,,0000,0000,0000,,lecture, induction is a lot more
Dialogue: 0,0:08:48.21,0:08:52.46,Default,,0000,0000,0000,,problematic than deduction.