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Aristotle once described humans as “therational animal.
” Well, actually, he said that “man is therational animal, ” but we don’t have to be sexist just because he was.
And if you’ve ever gotten into an argumentwith someone about religion or politics or which Hemsworth is the hottest, then you’ve experiencedhow irrational people can be about their opinions.
But what Aristotle meant is that rationalityis our distinguishing characteristic – it’s what sets us apart from the beasts.
And no matter how much you disagree with someoneabout God or Obama or Chris Hemsworth, you can at least grant that they are not beasts.
Because, most of the time at least, peoplecan be persuaded.
You use arguments all the time — in the comments, at family dinners, with your friends — you probably just don’t think of them the sameway that philosophers do.
When you try and convince your parents toloan you the car, or when you’re talking up Crash Course to your friends, you are usingarguments.
Thanks, by the way.
Each time you tell someone to do or believesomething — or when you’re explaining why you do or believe something — you are givingan argument.
The problem is, the vast majority of peoplearen’t really good at arguments.
We tend to confuse making a good argumentwith, 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 reasoningwill not only make you a better philosopher, it will also set you up to be a more persuasiveperson.
Someone who people will listen to.
Someone who’s convincing.
So, yeah, these skills are beneficial no matterwhat 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 youshould 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 calleda tripartite soul – what you might think of as your “self, ” or your psyche, dividedinto three parts.
First, there’s the rational, or logicalpart of the soul, which represents cool reason.
This is the aspect of your self that seeksthe truth and is swayed by facts and arguments.
When you decide to stop eating bacon for twomeals a day because, as delicious as it is, it’s bad for you, then you make that decisionwith the guidance of the rational part of your soul.
But then there’s the spirited aspect, oftendescribed as the emotional part of the self, although that doesn’t really quite captureit.
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 righteousanger at injustice, the part that drives your ambition, and calls upon you to protect others.
It gives you a sense of honor and duty, andis swayed by sympathy.
So if you decide to stop eating bacon becauseyou just finished reading Charlotte’s Web, and now you’re in love with Wilbur, thenyou’re being guided by the spirited part of your soul.
But we share the next part of our soul withother animals, be they pig, or moose, or aardvark.
The appetitive part is what drives you toeat, 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 justEAT ALL THE BACON because it just smells so dang good, the appetitive aspect of your soulis in control.
Now, Plato believed that the best human beings– and I should point out here that Plato most definitely did believe that some peoplewere better than others — are always ruled by the rational part of their soul, because it worksto keep the spirited and the appetitive parts in check.
People who allow themselves to be ruled bytheir spirited or appetitive selves are base, he believed, and not fully, properly human.
Now, most of us don’t buy into the conceptof the tripartite soul anymore — or the idea that some humans are less human than others.
But we do understand that we’re all motivated byphysical desires, emotional impulses, and rational arguments.
And philosophers continue to agree with Platothat reason should be in the driver’s seat.
So, how do you know if you’re good at it?How can you test your reasoning? Well, let’s head over to the Thought Bubblefor some Flash Philosophy.
Throughout this course, we’re going to apply ourphilosophical skills by pondering puzzles, paradoxes, and thought experiments.
Because remember: Philosophers love thinking aboutquestions — especially ones that don’t have ready answers.
So think of these exercises as philosophicalwind-sprints — quick tests of your mental abilities.
And here’s a doozy, from 20th century Britishthinker Bertrand Russell, one of the pioneers of what’s known as analytic philosophy.
Say there’s a town in which all men arerequired by law to be clean-shaven.
This town has only one barber, a man, who must followstrict rules: Rule number one: He must shave all men whodo not shave themselves.
Rule number two: He must not shave any manwho does shave himself.
It’s the nightmare of every libertarian and everymustachio’d hipster.
But here’s the question: Does the barber shave himself? Cause think about it: The barber only shavesmen who don’t shave themselves.
So if he does shave himself, then he must not, because the barber’snot allowed to shave guys who shave themselves.
But, if he doesn’t shave himself, then he hasto be shaved by the barber, because that’s the law.
Russell came up with this puzzle to illustrate thefact that a group must always be a member of itself.
That means, in this case, that “all menwho shave themselves” has to include every guy who shaves himself, including the barber.
Otherwise, the logic that dictates the group’sexistence 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 we’re ruledby good, sound, not-flawed reason? By perfecting the art of the argument.
An argument, in philosophy, isn’t just ashouting match.
Instead, philosophers maintain that your beliefsshould 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, aslong 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 speciesof arguments.
Probably the most familiar, and the easiest to carry out, is the deductiveargument.
The main rule of a deductive arguments is: if yourpremises are true, then your conclusion must be true.
And knowing that something is actually trueis very rare, and awesome.
So, here’s a boiled-down version of a gooddeductive argument: Premise 1: All humans are mortal.
Premise 2: Socrates is a human.
Conclusion: Socrates is mortal.
This kind of reasoning, where one fact leadsto another, is called entailment.
Once we know that all humans are mortal, and thatSocrates is a human, those facts entail that Socrates is mortal.
Deduction begins with the general – in thiscase, what we know about human mortality – and reasons down to the specific – Socratesin particular.
What’s great about deductive arguments isthat the truth of the premises must lead to the truth of the conclusion.
When this happens, we say that the argumentis valid – there’s just no way for the conclusion to be false if the premises aretrue.
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 humanmortality can prove that Socrates was Plato’s teacher.
As you might have noticed, there are plentyof mortal humans who never taught Plato.
What’s interesting, though, is that thisargument does happen to have a true conclusion, which leads us to another issue.
And thatis: Validity is not the same as truth.
All ‘valid’ really means is that if the premisesare true, then your conclusion can’t be false.
But that doesn’t mean that yourpremises prove your conclusion to be correct.
Like, in the case of whether Socrates wasPlato’s teacher, the premises are true, and the conclusion is true, but the argumentis still not valid — because the premises don’t in any way prove the conclusion.
Itjust happens to be true.
So, if your premises don’t guarantee the truth of yourconclusion, 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 mycat, this is invalid because the conclusion doesn’t entail from the premises…at all.
I mean, all cats are mammals, but all mammalsaren’t cats.
Which means there are such things as non-cat mammals, which I am justone example of.
And it probably goes without saying, but you canhave 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 premisesentail 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’thave a tail — I’ve seen him in a bathing suit — this argument is not deductively sound.
And a deductively sound argument is one that’sfree of formal flaws or defects.
It’s an argument whose premises are alltrue, and that’s valid, which means its conclusion is guaranteed to be true.
So, sound arguments should always be yourgoal.
The reason that deduction is prized by philosophers– and lots of other important kinds of thinkers — is that it’s the only kind of argumentthat can give you a real certainty.
But it’s limited, because it only works if you’re startingwith known, true premises, which are hard to come by.
And for what it’s worth, deductive truthsare usually pretty obvious.
They don’t tend to lead us to startlingly new information, like the factthat I’m not a cat, or that John doesn’t have a tail.
So instead of starting with premises thatare already certain, like deduction does, you’re gonna have to know how to determinethe truth of, and your confidence in, your premises.
Which means you’re going to have to acquaintyourself with the other species of arguments, which we’re 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: deductivereasoning.
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