How to Argue – Induction & Abduction: Crash Course Philosophy #3
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How to Argue – Induction & Abduction: Crash Course Philosophy #3

Crash Course Philosophy is brought to you
by Squarespace. Squarespace: Share your passion with the world. How do you know that aspirin will take care
of your headache? Why do you really want to see the new Marvel movie,
even though you haven’t heard anything about it, good or bad? Your ability to do things like predict how
a medication will affect you, or what movie you might like, or even things like what the
perfect gift might be for your best friend, or what’s the fastest way to get to campus
–- all of this stuff, you know through induction. Deductive arguments are great because they
give us certain answers. But unfortunately, much of the world cannot
be summed up in a neat deductive proof. Deduction requires a fair amount of general
information to give you a specific conclusion that is, frankly, probably kind of obvious. So, philosophy — and basically, you know, life as well —
require that you have other ways of reasoning. In addition to knowing how one fact leads
to another, you also need to take what you’ve experienced before, and use that to predict
what might happen in the future. And you need to be able to rule out what can’t
be true, so you can focus on what can. Through these kinds of reasoning, you’re
not only able to figure out stuff like how to fix your headache, and why your roommate
might be acting weird. You can also come up with better, more skillful arguments — and
counterarguments — which are some of the most important maneuvers in the philosophical
game. And maybe the best part is, you already know
how to use these techniques. In fact, I bet you’ve used them this very
day. You know this! [Theme Music] If you possess any ability to really predict the
future, it lies in your ability to reason inductively. Inductive reasoning relies on the predictability
of nature to reveal that the future is likely to resemble the past, often in important ways. For example, there’s tons of research to
support the knowledge that aspirin — acetylsalicylic acid — is an effective treatment for pain,
like headaches. And you probably have personal experience
with the effects of aspirin, too. So, you believe that this aspirin tablet will
cure the headache you have right now, because countless aspirin tablets have cured countless
headaches in the past. Likewise, you want to see the new Marvel movie,
because you liked most of the other ones, so you believe that they’ll continue to
deliver for you, entertainment-wise. But it’s important to remember that, unlike
deduction, where true premises entail true conclusions, inductive premises only mean
that the conclusion is likely to be true. Inductive arguments don’t provide you with
certainty. Instead, they work in terms of probabilities. And they’re useful for more than predicting
what’s going to happen. For example: Most men in ancient Athens had beards.
Socrates was a man who lived in ancient Athens. Therefore, Socrates probably had a beard This is an inductive argument, because it
starts with what we already know – about the grooming habits of ancient Athenian men,
and about the time and place in which Socrates lived – and makes an educated guess based
on that information. There’s no guarantee that the conclusion is correct,
but what’s known would seem to support it. Reasoning like this is incredibly useful, which is
why it’s so common. But there’s also a problem. The future doesn’t always resemble the past.
And every pattern has its outliers. So induction always has the potential to produce
false results. Aspirin might not work on a really bad headache. The new Marvel movie
might be awful. And, yeah, maybe a specific guy in Athens had a beard but it’s possible
he didn’t! While the world tends to work according to
predictable rules, sometimes those rules are violated. And you know what you need when that happens?
A little Flash Philosophy. Off to the Thought Bubble. Contemporary American philosopher Nelson Goodman
confronts the problems of induction, using a thought exercise about a hypothetical substance
called grue. According to Goodman’s scenario, grue is
anything that’s the color green before a certain time, a time that we will call t. And another property of grue is that, while
it’s green before time t, it’s blue after it. Now, let’s assume that we’re living in
a time before t. T could happen a hundred years from now or tomorrow, but we know that
all of the emeralds we’ve ever seen are green So, inductive reasoning lets us conclude that
all emeralds are green, and will remain green after time t — since emeralds haven’t been
known to change color. BUT! All emeralds are grue! Because it’s not yet time t,
and they’re green, which is part of the definition of grue. So we have no choice but to conclude that
the emeralds will be blue after time t arrives. Now we’ve got a problem. Because inductive
reasoning has led us to conclude that emeralds will be blue after time t, but inductive reasoning
also tells us that they’ll remain green. Goodman’s riddle reminds us that inductive
evidence can be flawed, or contradictory. It can make you think that you can predict
the future, when of course you can’t. So, there are times when you need to get at
the truth in other ways. Like by eliminating what’s obviously not true, and considering
what’s most likely. And for this, we turn our attention to one
of the most important philosophical figures of 19th century England: Sherlock Holmes. In chapter six of Sir Arthur Conan Doyle’s “The
Sign of the Four,” Mr. Holmes says, and I quote: “When you have eliminated the impossible, whatever
remains, however improbable, must be the truth.” This is probably the best, most succinct description
ever given of the kind of reasoning known as abduction. Which I know, it sounds like we’re talking
about a kidnapping or something, but abduction is a thought process sometimes described as
“inference to the best explanation.“ Abduction doesn’t reason straight from a premise to
a conclusion, as we’ve seen in deduction and induction. Instead, it reasons by ruling out possible
explanations until you’re left with the most plausible one, given the evidence. Consider
this: Anna told you she failed her physics midterm. Anna hasn’t been in physics class since
your teacher graded the exams. Anna has been in sociology class, which meets
right after physics. Anna dropped physics. Now, with only these premises, we can’t
deductively or inductively prove our conclusion – that she dropped physics. But, it’s a justifiable conclusion, because,
given what we know, dropping the class is the most plausible explanation of events. We know she’s not sick – because she’s
still going to sociology – and we know she had good reason to withdraw from the class,
because she was unlikely to pass. Concluding that she dropped the course makes
the most tidy use of our information, without leaving any loose ends. So let’s look at
another one: You and your roommate ate sushi last night. You both wake up with violent stomachaches. You and your roommate ate some bad sushi. The mere fact that you’re both sick doesn’t
prove that the sushi caused the sickness. But, given that you both ate the same thing
and you both have the same symptoms – absent other information, like that a stomach virus
is going around your dorm – the best explanation is that the sushi caused your intestinal anguish. Now, like induction, abduction doesn’t give
us certainty. But it is a really useful way to get through
puzzling situations when you don’t have clear evidence from the past to help you out. Doctors use abduction a lot when they’re
diagnosing illnesses, and detectives of course use it when piecing together evidence. You probably use it pretty often too – just
beware, because abduction must be used carefully! It uses only information you have at hand
— that’s why doctors and detectives work so hard to dig up more data, and re-create events from
the past, so they can help draw better conclusions. All right, now that we’ve looked at some
argument types, let’s find out how philosophers use arguments to interact with each other. Because, philosophers don’t argue like other
people do. It’s not like the conversation you have
around the dinner table about whether the Patriots are better than the Seahawks, or
why plain M&Ms are superior to peanut, which is clearly a preposterous position to take. Philosophers hold each other to different,
higher standards. They don’t teach each other get away with
saying, “I reject your argument because I don’t like its conclusion.” Or, “That’s
preposterous, peanut M&Ms are so good.” Instead, if you disagree with a conclusion,
you need to give reasons, just like the first person did when they made their case. Both people involved in this kind of exchange
are known as interlocutors, because we have to name everything. The first one advances
an argument, and the second one can either accept it, or offer a counterargument, which
is just what it sounds like – an argument offered in opposition to another argument. Think back to Socrates and the beard. You think Socrates had a beard, and your reasoning
is that most men in his time and place had them. I, however, think you’re wrong. So I give
you a counterargument. Gorgias, a contemporary of Socrates, said
Socrates couldn’t grow a beard and that he would sneak into barbershops and steal
discarded clippings to fashion fake beards for himself. Therefore, Socrates didn’t
have a (real) beard. And I just want to point out that this is
an actual philosophy conspiracy theory. Gorgias was a real guy, who differed with
Socrates on many things, and the dispute was said to have gotten personal. According to accounts of the time, Gorgias
actually spread the rumor that Socrates wore, like, a beard-wig, in an effort to shame and
discredit his rival. I mean, how could you be a good thinker if you weren’t a good
beard-grower. Gorgias’ gossip didn’t go over well with
everyone, and in this instance, let’s say you are skeptical about it too. So you counter my counterargument with a counter-counterargument. Gorgias was known for being a gossip, and
for hating Socrates, and trying to make him look bad. His fake beard tale seems wildly
unlikely. Therefore, we can’t take Gorgias’ statement seriously, so we should fall back
on the best information we have, which is that most of the men in his time and place
had beards. And as you can see, arguments of different
styles can be used in the same exchange. Like, the original argument, about Socrates
probably having a beard, was inductive. But this last counterargument is abductive.
And that’s fine. Arguments are meant to be useful, so we don’t have
to use the same kind of reasoning when we argue. This way of exchanging ideas through dialogue
was popularized by Socrates, and so has become known as the Socratic method. Socrates thought dialogue was the best way
to learn, and to get at truth. And it’s important to note that, while philosophers
have a reputation for being an argumentative lot, they don’t think of the Socratic method as
something that results in a winner and a loser. Rather, it’s an exercise that brings both
interlocutors closer to the truth. The goal of the philosopher is not to win,
but to find truth, so you shouldn’t be disappointed if someone presents a counterargument that
you can’t find a response to. When that happens, a good philosopher will
be grateful to their interlocutor for helping them reject false beliefs and build stronger
ones. Today you learned about two more types of
philosophical reasoning, induction and abduction. You’ve seen their strengths, and their weaknesses.
And you’ve also learned about counterarguments, and the Socratic method. This episode is brought to you by Squarespace.
Squarespace helps to create websites, blogs or online stores for you and your ideas. Websites
look professionally designed regardless of skill level, no coding required. Try Squarespace at for a special offer. Crash Course Philosophy is produced in association
with PBS Digital Studios. You can head over to their channel to check out amazing shows like
BrainCraft, It’s OK To Be Smart, and PBS Idea Channel. This episode was filmed in the Doctor Cheryl
C. Kinney Crash Course Studio with the help of these amazing people and our Graphics Team
is Thought Cafe.


  • BoosterMcFlames

    Hi, i don't seem to understand that concluding that the emeralds will become blue after time t is "inductive reasoning" (using past experience to make future predictions.) anyone cares to explain to me how is it inductive ?

  • Richard Deese

    As an interim point, I do not believe aspirin will cure my headache. This is a non-sequitur. The active ingredient in aspirin, acetylsalicylic acid, is used as an NSAID (non-steroidal anti-inflammatory drug), and as a blood thinner. The simple fact is, if some drug company (or anyone, for that matter) tried to get aspirin through the FDA's drug trials as a pain reliever today, it would fail – miserably. It was 'grandfathered' in, because it had been used for so long, and because people trusted it, and because there was already so much of it out there, and it didn't cause any actual harm, they just decided to accept it without rigorous trials. If you want to relieve pain, use acetaminophen or ibuprofen. Those actually do relieve pain. Rikki Tikki.

  • Richard Deese

    Given the facts that, a) Not all people like peanuts, and, b) An ever-increasing number of people are allergic to peanuts, I conclude that, c) Liking peanuts is a matter of taste, and, d) An ever-increasing number of people can't eat them regardless. As for myself, I'm not allergic to peanuts. I simply prefer cashews, pecans, hazelnuts, macadamias, and any number of other nuts besides peanuts. I also propose that at least part of peanuts' popularity is due to the fact that they're so much cheaper than most other nuts. Cheaper is not better, but it can make something more prevalent. That's why M&Ms have them. Rikki Tikki.

  • Human Errer

    I think abductive reasoning should be used as a precursor to deductive reasoning in order to give one a fairly stable starting point. That’s about the extent of it’s worth, as far as I’m concerned.

  • Jimmy Gravitt

    WTF? Was that Motrin? That's not aspirin. I can't believe you would lie to us john… hank… Green(e?) brother from Sci Show….

  • Molly Stringer

    Hey thought cafe: I loved the iron man and captain american animation at the beginning and it made me laugh way more than was probably necessary. Great job, guys! (on everything you do, not just that one animation)

  • CGMe

    If Avengers Civil War simply consisted of people slapping each other, as per the video, then I would have enjoyed it more. (I just used a conditional existential statement 🙂 )

  • Lisa Meskimen

    So is the main difference between inductive and abductive arguments that abductive arguments use specific events as premises? The two forms seem very similar to me. My philosophy professor said that Sherlock Holmes uses the inductive method, but it seems that he also uses the abductive method.

  • Latter-day Canadian

    In your last video you talked about hard truths being used for deductive reasoning but would using circumstantial hard truths be considered inductive?

    Truth: all planets have gravity
    Truth: Earth and Mars are both planets
    Truth: Gravity is fixed at a constant rate
    Truth: I can currently jump 30 centimetres high on planet earth

    Conclusion- because both planets have fixed rates of gravity I can jump 30 centimetres in the air on either earth or Mars

  • Shouki Fong

    I wish more people (including myself) learned to argue like a philosopher. Not arguing to win but merely to get closer to the truth.

  • Victor Cleemonts

    I think using man to refer to all of humanity isn't sexist. The word when referring to humanity is a shortening of mankind. Man is present in both woman and man and so should refer to eachother equally.

  • M M

    Hah, Intro to Logic and Reasoning Philosopher Style should be established as a required class in high school… and college… Maybe even middle school

  • Михаил Тарабанько

    The video is misleading.
    1. Most men in ancient Athens had beards.
    2. Socrates was a man who lived in ancient Athens.
    Therefore, Socrates probably had a beard.
    This argument is a deductive one. It holds true regardless of whether Socrates had beard or not.

  • leterrible 87

    Don't get me wrong I absolutely love these Crash Courses, but does anyone else see the comical irony in a channel that promotes intellectualism sponsoring [seemingly very little skill required] stuff like SquareSpace? lol


    If you don't know how nature works you are ignorant and should learn how nature works so as to not ruin your children from being like you. Ignorant.


    Nature goes on forever for everyone and everything to return as everyone and everything an infinite number of times. 😱😫😰


    The goal of the philosopher is to find the truth that if you and your opponent cannot find the truth then both of you are not wrong until one of you finds the truth. When you have found the truth and cannot make the other person comprehend it is when you should leave your family and friends for higher company.

  • Awwhamburgerz

    The idea of someone preferring plain m&m’s over peanut unless they have an allergy was the most confusing thing I’ve heard on this channel yet.

  • AvangionQ

    The one thing about arguments that consistently annoys me is when a false premise is presented as truth … always leads to erroneous conclusions.

  • Dijon Moutard

    I don't get the Grue thought-experiment. 

    Let Grue be a substance that is green before time t and blue after time t. Say time t is tomorrow.
    All emeralds are green before time t; because tomorrow has not yet arrived.
    Therefore all emeralds are Grue (?), and will be blue tomorrow.

    The conclusion just doesn't follow from the premises, because "emeralds" only fit a part of the definition of "Grue", and there is no reason to believe they would fit the whole definition.

  • Damien Stone

    Lets put are skills to use and have a real debate. Anyone… Maybe 911? Or… Socialism? Or… Euthanasia/abortion?

  • Scatttyyy R

    The socrates beard argument is deductive. It is necessarily true that Socrates probably had a beard. This is the foundation of statistically validity

  • male6561

    Didn't we learn in the last video that all the premises could be true, and still lead to a false conclusion? Then how can we say that the conclusion from deduction is true? Isnt it only probably true, and therefore all deduction is actually induction?

    And what was that Grue thing about? Was it that we cant know if things around us are Green or Grue before t, and likewise if the Blue stuff around us are Blue or Grue past t?

  • male6561

    Gorgias Abduction:
    Premise 1: Most great thinkers have great beards
    Premise 2: Socrates doesnt have a great beard
    Conclusion: Socrates isnt a great thinker.

  • Gabriella M

    I live for the comment section here. I read it dumbfounded at all of the philosophical language acting as if I actually UNDERSTAND what's going on 🙂

  • 714Sluggo

    Actually the idea that Gordias claimed Socrates wore a fake beard should give credence to the idea that Socrates really did have a beard. Even if Gordias was lying about Socrates, the fact that he tried to mock Socrates beard as false implies and almost states that Socrates indeed had some groovy Greek facial hair! (What kind of reasoning was that eh?)

  • Mark mywords

    Our boss is a nasty piece of work; he employed my manager; therefore I will get screwed. Surely this is both deductive and inductive.

  • Michael Nelson

    Really enjoying what I'm learning with all these videos, but I'm concerned about forgetting a lot of things. Is there a site with something to download/print?

  • Ben Wil

    4:38 not sure how good an example Holmes is. For instance it’s incredibly arrogant to assume you know ALL the ‘impossible’ so to say whatever remains must be the truth is completely false because you can’t know for sure that you eliminated all the impossible.
    Besides that thank you for the awesome vids

  • Harry H

    I induce that you have 200 dislikes because there are absolutely no pauses or breaks in between your sentences. its uncomfortable to listen to this.

  • I wish I was wrong

    Why does he keep referring to a philosopher as she? I'm not sexist, I've just never, ever herd of a female philosopher. So I'm wondering how deep pc culture has gone.

  • Cainyoyo

    "In fact I bet you've used them this very day. You know this."
    Even if you said "No John, I haven't used them today…." then you have used it today.
    My mind is blown.

  • Johnathan Roan

    I argue like a philosopher but that’s just because I’m someone that reflects on a lot of things so think about it in more ways. I hate people that don’t argue like philosophers because they assume their right only by discrediting (as in making it seem like it’s not worth listening to) anything that’s against what they say like a lot of the political climate now and they will use those flawed arguments you mentioned in the last lesson. It’s so frustrating. Even in some cases when the conclusion is not bad but I can’t agree with it because the reasoning is good but the conclusion to solve the problem just doesn’t line up. There are some cases like that in some feminism and LGBTQ points. I agree with them but up until some conclusions of how they go about things. It’s like this

    Them “these are the reasons why we think this way”

    Me “okay that’s valid”

    Them “this is how we fix that problem”

    Me “oh well that’s not good the world isn’t that simple. Your solution has a chance of new problems. You can’t command people to be different”

    Them “we’re unable to come up with a valid counter so you’re the problem”

    Me “buddy I’m the reality. If that’s your problem then for your sake I’m sorry you were born into this reality.”

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