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We received a wonderful example of -- for
the kinds of bargains we studied

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in the weeks on inductive reasoning.

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We studied generalization, and we studied
applications of those generalizations.

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And using that for causal reasoning that
we tested by manipulations

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and by the sufficient condition tests,

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and all of those are brought together 
in a wonderful little video.

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So, take a look.

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>> Hello.

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My name's Catriona, and I live in Sweden.

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I've spent many years, eating a little bit
of chocolate everyday.

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And I've always strongly believed that
eating chocolate makes you happier.

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In other words, most people will be 
in a better mood

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after they've eaten chocolate 
than before.

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And I'll give you four pieces of evidence

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in support of my conclusion.

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Evidence one: I've met a lot of people
over the years

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and when I give them some of my chocolate, 
they always seem happy about it.

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I can't think of a single case 
of someone eating chocolate

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who hasn't looked satisfied afterwards.

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Evidence two: It could be that

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eating chocolate isn't really causing
their happiness.

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They're just happy people eating
chocolate.

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So, I asked unhappy people whether they
ever eat chocolate.

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And they confirmed that they do, 
precisely because it cheers them up.

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Evidence three:

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Now, I went to a chocolate factory where
the workers get free chocolate every day.

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And these people could theoretically be
unhappy like the rest of us could.

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but they all had smiles on their faces,
and some smears of chocolate.

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Evidence four: You may ask whether these
people are also in love

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and it's love that's causing
the happiness,

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not actually the chocolate.

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So I had to find people who eat chocolate,
but are not in love.

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I did a mini survey at my corner shop.

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And 80% of the people who responded that
they were not in love,

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reported that they definitely felt 
their mood improve

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when they ate chocolate.

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So, it does seem to be the case that

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eating chocolate is probably sufficient 
to improve your mood.

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Obviously there are people who never eat
chocolate and are very happy.

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For example a successful dieter 
or your dentist.

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You can find happiness by falling in love
or getting promoted

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or finally reaching the top of Mt.
Everest, whatever's your biggest dream.

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But for an instant helping of happiness,

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chocolate will cheer you up, mm.

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>> Wasn't that great?

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I already knew that I loved chocolate

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and that it improved my mood,

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so maybe I was convinced 
by this argument

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because, I already believed 
the conclusion.

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And that's when you ought to be careful.

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When you look at an argument, and it's for
a conclusion you already believed,

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then there's going to be a tendency 
to think it's a great argument.

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so if you really want to know

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whether it is or is not a good argument.

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You gotta look carefully at the ones that
are trying convince you

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of things that already had a tendency to
believe in the first place.

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So let's look carefully at her conclusion.

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Catriona's conclusion was very carefully
qualified.

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On the one hand, she said that chocolate
is one of the things that makes you happy.

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She doesn't claim that it's the only thing

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that makes you happy: you know,

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Love might make you happy, climbing 
Mount Everest might make you happy,

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all kinds of things can make you happy.

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She's only claiming that 
chocolate's one of them.

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Another qualification, is that she says

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chocolate will probably 
improve your mood.

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She don't say it's definitely,

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don't say it works always, 
or for all people.

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But it'll probably improve your mood:
so it's an inductive argument,

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and she doesn't have to prove it 
beyond a shadow of a doubt.

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That's a good move in an argument, 
because it's very hard to prove things

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beyond a shadow of a doubt.

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But there is one part of her conclusion
that makes the argument difficult.

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And that's that she says chocolate
improves your mood.

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Now that's a causal claim.

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That's not just that you eat chocolate 
and you also happen to be happy.

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That's that eating chocolate causes you

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to be happier than you were before,

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that is, to be in a better mood 
than you were before.

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So let's see if the different bits of 
evidence that she presents

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really do support that conclusion.

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So the first bit of evidence 
that Catriona provides is this.

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"Now I've met a lot of people, over the
years, and whenever

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I give them some of my chocolate they're
clearly happy about it."

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What kind of argument is that?

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That is a statistical generalization 
from a sample,

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because she hadn't met 
everybody in the world,

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she's only met some people.

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But the sample that she's been able to
check, they've all liked chocolate.

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She adds one more claim:

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"I can't think of a single case of 
someone eating chocolate

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and not looking satisfied afterwards."

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You know, this is kind of repetitious,

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because she says 
she can't think of a case.

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She just told you that whenever she gives
them chocolate, then they're happy

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and if they're happy they're satisfied,
and so maybe that doesn't add too much.

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It's still a generalization.

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What are we going to think about this
generalization?

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Well, let's assume that 
she's got a lot of friends.

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So, she's checked a lot of people, she's
given a lot of people chocolate

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and -- and they're all happy.

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Well, is the premise true?

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Well, do we believe 
that every single person

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that she gave chocolate to 
was satisfied and happy?

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I kind of tend to doubt that, Catriona, 
sorry, but --

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it's just, such uniformity is unusual 
among human beings.

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And so my bet is that a couple of them
didn't.

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But notice that she didn't really need
that, because

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she's only arguing that giving chocolate 
will probably improve your mood,

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not that it always will for everybody.

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So she doesn't need that strong claim
about everybody.

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So she's still on pretty firm ground with 
regard to claiming that almost everybody,

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or most of the people, have improved their
mood when she gave them chocolate.

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We still might worry about a bias sample.

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There might be some cultures out there, 
or some types of people out there,

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that don't like chocolate.

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Maybe they're allergic to chocolate,

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or something like that, 
that would be really sad,

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I'm sorry to even think about that, 
it makes me sad.

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But, there probably are, and they're
people that don't like chocolate.

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And so, it's not going to work for them.

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So maybe she wants to qualify her
conclusion a little bit, you know,

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"among the groups that I've met:

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different cultures might be different,

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different biological conditions might make
people allergic to chocolate."

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But, with regard to most of the people
she's met,

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chocolate seems to work pretty well.

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So we've got now a statistical
generalization:

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"Most people, if you give them chocolate, 
it improves their mood."

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Great.

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What does that show you about you, because
remember her conclusion is

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that if you have chocolate, then that
chocolate will probably improve your mood.

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So now she needs to take that
generalization

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and apply it back down 
to you as an individual,

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to make a prediction about what'll happen
to you if you eat some chocolate.

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So in this particular bit of evidence, she
needs to generalize up

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to "most people will have their mood
improved

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if they eat chocolate," and then back down
again.

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And since that's true with most people,

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and you're not special in any particular
way

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-- or it would be a conflicting 
reference class fallacy --

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since you're not special 
in any particular way,

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the chocolate will also improve 
your mood.

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That's the way this first bit of evidence
seems to go.

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So now we're ready for her second bit of
evidence.

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Let's get all adjusted here

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so that we can think about this new 
bit of evidence that Catriona provides.

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Okay, what she says is:

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it could be that chocolate isn't really 
causing the happiness.

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Maybe they were just happy 
before eating the chocolate.

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Now, that's a problem.

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If you're going to say that it improves
people's moods

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when they eat chocolate,

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it's not good enough 
that people are already happy,

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and then that makes' em want to eat
chocolate.

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And so they eat chocolate to celebrate how
happy they are.

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Well you gotta prove that it actually does
cause the improvement in the mood.

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Okay, how are you going to do that?

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Well, we looked, in the lectures on
induction, at causal reasoning.

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What you need to do is manipulate.

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You want to look at people who are not
happy

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and see if the chocolate makes them 
go up in mood

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and manipulate the amount of chocolate,
manipulate how happy they are,

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and see how those have effects 
on each other.

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And that's how you decide among the
hypotheses.

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And that's exactly what

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Catriona does.

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"So I asked some unhappy people
whether they ever eat chocolate,

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and they confirmed that they do,
precisely because it cheers them up."

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Ah, so now we have a sample of people, 
where we've manipulated their happiness.

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We've looked at happy people and unhappy
people.

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We've looked at people at times 
when they're happy

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and times when they're unhappy.

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And then we can look at their chocolate
consumption

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and we can check to make sure 
that they're happier afterwards.

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It's just like 
checking whether smoking causes cancer.

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We talked about that in the lectures on
induction.

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If you want to know 
whether smoking causes cancer,

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what you do is you induce smoking 
in creatures

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-- in this case, lab monkeys -- 
that did not previously smoke

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and see whether that increases 
their cancer rate.

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And what she's doing is she's saying:

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"let's take people that 
don't have happiness,

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give them chocolate, and see 
if that increases their happiness."

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So she's using exactly the kind of
manipulation test

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that we talked about 
in the lectures on induction.

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Good job, Catriona.

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Now let's switch to the fourth bit of
evidence,

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and I want to get ready for that one too.

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Now, what Catriona says for her fourth
bit of evidence is:

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"you may ask, what if all these people 
are also in love,

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and it's love that's making them happy, 
not really chocolate?"

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Because remember, 
she doesn't want to claim

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chocolate's the only thing 
that makes you happy.

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Love might be sufficient for happiness,

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just like chocolate 
also causes happiness.

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How are we going to tell which one it is?

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Well, in the lectures on causal
reasoning,

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when we were looking at the tables,
and the diners who died

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from the poisoned food, 
one of the points that we made

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was that if you have two candidates 
for a sufficient condition,

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you've gotta look at situations 
where one of them is present

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without the other and the other present
without the first one.

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And that's exactly what Catriona does.

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She says, I had to find people who eat
chocolate, but are not in love.

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Whoa, well that's what 
you're looking for,

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because if you have some people 
who eat chocolate,

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but are not in love,

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and some people who are not in love 
but eat chocolate, you can test it.

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And what did she find?

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Well: "I did a mini-survey 
outside my nearest corner shop,

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and 80% if the people who confessed

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that they were not in love

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said they definitely felt their mood 
improve when they ate chocolate.

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Notice she's not claiming it's so
universal, 100% anymore,

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she's down to 80%: 
good move.

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But in addition, she's now ruled out that
it's really the love

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that's the only sufficient condition: 
even when the love's not present,

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you still get happiness 
with eating chocolate.

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So that's applying one of the tests that
we talked about

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in the section on causal reasoning to test
for sufficient conditions.

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Okay, we've done our bits of evidence one
and two and four.

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We skipped over number three.

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So what's your third bit of evidence?
Now, we've gotta look at that one.

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Okay, what Catriona says is: 
"I went to a chocolate factory

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where all the workers 
eat chocolate every day."

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Not only that, it's free.

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Free chocolate! Yeah, mm!

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I love it.

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"Like everyone else, these people could
theoretically be unhappy,

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but they have smiles on their faces."

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Wouldn't you?

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Free chocolate all day long.

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But wait a minute, wait a minute:
is this a good argument?

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Like I said, it's a conclusion I like.

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But we still gotta look at it critically.

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Sorry, Catriona, 
these people are happy,

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but how do you know that they're happy
because of the chocolate, right?

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They've got a job in the factory,
It's good having a job.

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Chocolate's very popular, so maybe the
factory's doing really well,

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which means they can pay them 
more money, better benefits, good job:

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maybe that's what's making them happy?

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00:13:50,320 --> 00:13:52,520
Sure, all these people in the factory 
are happy.

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But it might not be the chocolate.

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It might be the fact 
that they got a good job.

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00:13:58,650 --> 00:14:03,782
So I think this fourth bit of evidence is
not really all that strong.

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Her number three, by the way:
the fourth one we considered.

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It's not all that strong:
now, what does that show you?

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You could say: 
"Wait a minute, she's got four arguments,

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one of them's no good, 
so it all is back to nothing.

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00:14:17,330 --> 00:14:19,760
But of course, that's not 
the right way to think about it.

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She gave us four bits of evidence.

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If one of them doesn't work, 
and we've only got three left,

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00:14:24,817 --> 00:14:26,420
we've still got three left.

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00:14:26,420 --> 00:14:32,090
So if those first three bits of evidence
are good, and if they show at least

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that it'll probably improve your mood,
and they establish

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the cause of conclusion that she claimed, 
then it seems to me

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she's given us pretty good evidence for
the conclusion she was claiming.

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And in doing so, she's exemplified a lot
of the different forms of reasoning

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that we studied in the weeks 
on inductive reasoning.

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So, thank you very much, Catriona,

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for submitting this wonderful video, 
this wonderful argument.

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We all learned from it 
and we appreciate it.