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  • Aristotle once described humans asthe rational animal.”

  • Well, actually, he said thatman is the rational animal,” but we don’t have to

  • be sexist just because he was.

  • And if youve ever gotten into an argument with someone about religion or politics or which

  • Hemsworth is the hottest, then youve experienced how irrational people can be about their opinions.

  • But what Aristotle meant is that rationality is our distinguishing characteristicit’s

  • what sets us apart from the beasts.

  • And no matter how much you disagree with someone about God or Obama or Chris Hemsworth, you

  • can at least grant that they are not beasts.

  • Because, most of the time at least, people can be persuaded. By arguments.

  • You use arguments all the time -- in the comments, at family dinners, with your friends -- you

  • probably just don’t think of them the same way that philosophers do.

  • When you try and convince your parents to loan you the car, or when youre talking

  • up Crash Course to your friends, you are using arguments. Thanks, by the way.

  • Each time you tell someone to do or believe something -- or when youre explaining why

  • you do or believe something -- you are giving an argument.

  • The problem is, the vast majority of people aren’t really good at arguments.

  • We tend to confuse making a good argument with, like, having witty comebacks, or just

  • making your points more loudly and angrily, instead of building a case on a solid foundation

  • of logic. Which can be harder than it sounds.

  • But learning about arguments and strong reasoning will not only make you a better philosopher,

  • it will also set you up to be a more persuasive person. Someone who people will listen to.

  • Someone who’s convincing.

  • So, yeah, these skills are beneficial no matter what you want to do with your life.

  • So you might as well know how to argue properly.

  • [Theme Music]

  • If you want to learn how to argue, then you should probably start about 2400 years ago,

  • when Plato was laying out how reason can, and should, function in the human mind.

  • He believed that we all have what he called a tripartite soulwhat you might think

  • of as yourself,” or your psyche, divided into three parts.

  • First, there’s the rational, or logical part of the soul, which represents cool reason.

  • This is the aspect of your self that seeks the truth and is swayed by facts and arguments.

  • When you decide to stop eating bacon for two meals a day because, as delicious as it is,

  • it’s bad for you, then you make that decision with the guidance of the rational part of your soul.

  • But then there’s the spirited aspect, often described as the emotional part of the self,

  • although that doesn’t really quite capture it.

  • The spirited soul isn’t just about feeling -- it’s also about how your feelings fuel your actions.

  • It’s the part that responds in righteous anger at injustice, the part that drives your

  • ambition, and calls upon you to protect others.

  • It gives you a sense of honor and duty, and is swayed by sympathy.

  • So if you decide to stop eating bacon because you just finished reading Charlotte’s Web,

  • and now youre in love with Wilbur, then youre being guided by the spirited part of your soul.

  • But we share the next part of our soul with other animals, be they pig, or moose, or aardvark.

  • The appetitive part is what drives you to eat, have sex, and protect yourself from danger.

  • It is swayed by temptations that are carnal, and visceral.

  • So at those times when you go ahead and just EAT ALL THE BACON because it just smells so

  • dang good, the appetitive aspect of your soul is in control.

  • Now, Plato believed that the best human beings -- and I should point out here that Plato

  • most definitely did believe that some people were better than others -- are always ruled

  • by the rational part of their soul, because it works to keep the spirited and the appetitive parts in check.

  • People who allow themselves to be ruled by their spirited or appetitive selves are base,

  • he believed, and not fully, properly human.

  • Now, most of us don’t buy into the concept of the tripartite soul anymore -- or the idea

  • that some humans are less human than others.

  • But we do understand that were all motivated by physical desires, emotional impulses, and rational arguments.

  • And philosophers continue to agree with Plato that reason should be in the driver’s seat.

  • So, how do you know if youre good at it? How can you test your reasoning?

  • Well, let’s head over to the Thought Bubble for some Flash Philosophy.

  • Throughout this course, were going to apply our philosophical skills by pondering puzzles, paradoxes, and thought experiments.

  • Because remember: Philosophers love thinking about questions -- especially ones that don’t have ready answers.

  • So think of these exercises as philosophical wind-sprints -- quick tests of your mental abilities.

  • And here’s a doozy, from 20th century British thinker Bertrand Russell, one of the pioneers

  • of what’s known as analytic philosophy.

  • Say there’s a town in which all men are required by law to be clean-shaven. This town

  • has only one barber, a man, who must follow strict rules:

  • Rule number one: He must shave all men who do not shave themselves.

  • Rule number two: He must not shave any man who does shave himself.

  • It’s the nightmare of every libertarian and every mustachio’d hipster. But here’s the question:

  • Does the barber shave himself?

  • Cause think about it: The barber only shaves men who don’t shave themselves. So if he does

  • shave himself, then he must not, because the barber’s not allowed to shave guys who shave themselves.

  • But, if he doesn’t shave himself, then he has to be shaved by the barber, because that’s the law.

  • Russell came up with this puzzle to illustrate the fact that a group must always be a member of itself.

  • That means, in this case, thatall men who shave themselveshas to include every

  • guy who shaves himself, including the barber.

  • Otherwise, the logic that dictates the group’s existence just doesn’t hold up.

  • And if the barber is a logical impossibility, then he can’t exist, which means the reasoning

  • behind his existence is inherently flawed.

  • And philosophy doesn’t tolerate flawed reasoning.

  • So, how do we make sure that were ruled by good, sound, not-flawed reason?

  • By perfecting the art of the argument.

  • An argument, in philosophy, isn’t just a shouting match.

  • Instead, philosophers maintain that your beliefs should always be backed up by reasons,

  • which we call premises.

  • Premises form the structure of your argument. They offer evidence for your belief, and you

  • can have as many premises as you like, as long as they support your conclusion, which

  • is the thing that you actually believe.

  • So, let’s dissect the anatomy of an argument.

  • There are actually several different species of arguments. Probably the most familiar,

  • and the easiest to carry out, is the deductive argument.

  • The main rule of a deductive arguments is: if your premises are true, then your conclusion must be true.

  • And knowing that something is actually true is very rare, and awesome.

  • So, here’s a boiled-down version of a good deductive argument:

  • Premise 1: All humans are mortal.

  • Premise 2: Socrates is a human.

  • Conclusion: Socrates is mortal.

  • This kind of reasoning, where one fact leads to another, is called entailment.

  • Once we know that all humans are mortal, and that Socrates is a human, those facts entail that Socrates is mortal.

  • Deduction begins with the generalin this case, what we know about human mortalityand

  • reasons down to the specificSocrates in particular.

  • What’s great about deductive arguments is that the truth of the premises must lead to

  • the truth of the conclusion.

  • When this happens, we say that the argument is validthere’s just no way for the

  • conclusion to be false if the premises are true.

  • Now check out this argument:

  • All humans are mortal. Socrates is a human. Therefore, Socrates was Plato’s teacher

  • That argument is invalid, because nothing about human mortality can prove that Socrates was Plato’s teacher.

  • As you might have noticed, there are plenty of mortal humans who never taught Plato.

  • What’s interesting, though, is that this argument does happen to have a true conclusion,

  • which leads us to another issue. And that is:

  • Validity is not the same as truth.

  • Allvalidreally means is that if the premises are true, then your conclusion can’t be false.

  • But that doesn’t mean that your premises prove your conclusion to be correct.

  • Like, in the case of whether Socrates was Plato’s teacher, the premises are true,

  • and the conclusion is true, but the argument is still not valid -- because the premises

  • don’t in any way prove the conclusion. It just happens to be true.

  • So, if your premises don’t guarantee the truth of your conclusion, then you can end up with some really crappy arguments.

  • Like this one: - All cats are mammals

  • - I’m a mammal - Therefore, I’m a cat

  • As much as part of me would like to be my cat, this is invalid because the conclusion

  • doesn’t entail from the premisesat all.

  • I mean, all cats are mammals, but all mammals aren’t cats. Which means there are such

  • things as non-cat mammals, which I am just one example of.

  • And it probably goes without saying, but you can have a perfectly valid argument and still have a false

  • conclusion, if any of your premises are false. For example: - All humans have tails

  • - My brother John is a human - Therefore, John Green has a tail!

  • The argument is totally valid! – Because the premises entail the conclusion! The reasoning totally stands up!

  • It’s just that one of the premises is flawed.

  • Since I’m reasonably certain that John doesn’t have a tail -- I’ve seen him in a bathing

  • suit -- this argument is not deductively sound.

  • And a deductively sound argument is one that’s free of formal flaws or defects.

  • It’s an argument whose premises are all true, and that’s valid, which means its

  • conclusion is guaranteed to be true.

  • So, sound arguments should always be your goal.

  • The reason that deduction is prized by philosophers -- and lots of other important kinds of thinkers

  • -- is that it’s the only kind of argument that can give you a real certainty.

  • But it’s limited, because it only works if youre starting with known, true premises, which are hard to come by.

  • And for what it’s worth, deductive truths are usually pretty obvious. They don’t tend

  • to lead us to startlingly new information, like the fact that I’m not a cat, or that John doesn’t have a tail.

  • So instead of starting with premises that are already certain, like deduction does,

  • youre gonna have to know how to determine the truth of, and your confidence in, your premises.

  • Which means youre going to have to acquaint yourself with the other species of arguments,

  • which were gonna do next time.

  • But today, we talked about the value of reason, the structure of arguments, and we took a

  • close look at one kind of argument: deductive reasoning.

  • This episode of Crash Course Philosophy is made possible by Squarespace. Squarespace

  • is a way to create a website, blog or online store for you and your ideas. Squarespace

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  • Crash Course Philosophy is produced in association with PBS Digital Studios. You can head over

  • to their channel to check out amazing shows like The Art Assignment, The Chatterbox, and Blank on Blank.

  • This episode of Crash Course was filmed in the Doctor Cheryl C. Kinney Crash Course Studio

  • with the help of all of these amazing people and our Graphics Team is Thought Cafe.

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議論の仕方 - 哲学的推論。クラッシュコース 哲学的推論 #2 (How to Argue - Philosophical Reasoning: Crash Course Philosophy #2)

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    羅紹桀 に公開 2021 年 01 月 14 日
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