Lecture 8-9 - A Student Example of Causal Reasoning about Chocolate

From the "Think Again: How to Reason and Argue" course on Coursera

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

in the weeks on inductive reasoning.

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

And using that for causal reasoning that
we tested by manipulations

and by the sufficient condition tests,

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

So, take a look.

>> Hello.

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

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

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

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

after they've eaten chocolate
than before.

And I'll give you four pieces of evidence

in support of my conclusion.

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

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

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

who hasn't looked satisfied afterwards.

Evidence two: It could be that

eating chocolate isn't really causing
their happiness.

They're just happy people eating
chocolate.

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

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

Evidence three:

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

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

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

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

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

not actually the chocolate.

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

I did a mini survey at my corner shop.

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

reported that they definitely felt
their mood improve

when they ate chocolate.

So, it does seem to be the case that

eating chocolate is probably sufficient
to improve your mood.

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

For example a successful dieter
or your dentist.

You can find happiness by falling in love
or getting promoted

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

But for an instant helping of happiness,

chocolate will cheer you up, mm.

>> Wasn't that great?

I already knew that I loved chocolate

and that it improved my mood,

so maybe I was convinced
by this argument

because, I already believed
the conclusion.

And that's when you ought to be careful.

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

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

so if you really want to know

whether it is or is not a good argument.

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

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

So let's look carefully at her conclusion.

Catriona's conclusion was very carefully
qualified.

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

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

that makes you happy: you know,

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

all kinds of things can make you happy.

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

Another qualification, is that she says

chocolate will probably
improve your mood.

She don't say it's definitely,

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

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

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

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

beyond a shadow of a doubt.

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

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

Now that's a causal claim.

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

That's that eating chocolate causes you

to be happier than you were before,

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

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

really do support that conclusion.

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

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

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

What kind of argument is that?

That is a statistical generalization
from a sample,

because she hadn't met
everybody in the world,

she's only met some people.

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

She adds one more claim:

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

and not looking satisfied afterwards."

You know, this is kind of repetitious,

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

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

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

It's still a generalization.

What are we going to think about this
generalization?

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

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

and -- and they're all happy.

Well, is the premise true?

Well, do we believe
that every single person

that she gave chocolate to
was satisfied and happy?

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

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

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

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

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

not that it always will for everybody.

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

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

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

We still might worry about a bias sample.

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

that don't like chocolate.

Maybe they're allergic to chocolate,

or something like that,
that would be really sad,

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

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

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

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

"among the groups that I've met:

different cultures might be different,

different biological conditions might make
people allergic to chocolate."

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

chocolate seems to work pretty well.

So we've got now a statistical
generalization:

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

Great.

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

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

So now she needs to take that
generalization

and apply it back down
to you as an individual,

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

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

to "most people will have their mood
improved

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

And since that's true with most people,

and you're not special in any particular
way

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

since you're not special
in any particular way,

the chocolate will also improve
your mood.

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

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

Let's get all adjusted here

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

Okay, what she says is:

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

Maybe they were just happy
before eating the chocolate.

Now, that's a problem.

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

when they eat chocolate,

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

and then that makes' em want to eat
chocolate.

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

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

Okay, how are you going to do that?

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

What you need to do is manipulate.

You want to look at people who are not
happy

and see if the chocolate makes them
go up in mood

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

and see how those have effects
on each other.

And that's how you decide among the
hypotheses.

And that's exactly what

Catriona does.

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

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

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

We've looked at happy people and unhappy
people.

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

and times when they're unhappy.

And then we can look at their chocolate
consumption

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

It's just like
checking whether smoking causes cancer.

We talked about that in the lectures on
induction.

If you want to know
whether smoking causes cancer,

what you do is you induce smoking
in creatures

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

and see whether that increases
their cancer rate.

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

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

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

So she's using exactly the kind of
manipulation test

that we talked about
in the lectures on induction.

Good job, Catriona.

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

and I want to get ready for that one too.

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

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

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

Because remember,
she doesn't want to claim

chocolate's the only thing
that makes you happy.

Love might be sufficient for happiness,

just like chocolate
also causes happiness.

How are we going to tell which one it is?

Well, in the lectures on causal
reasoning,

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

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

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

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

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

And that's exactly what Catriona does.

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

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

because if you have some people
who eat chocolate,

but are not in love,

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

And what did she find?

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

and 80% if the people who confessed

that they were not in love

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

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

she's down to 80%:
good move.

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

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

you still get happiness
with eating chocolate.

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

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

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

We skipped over number three.

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

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

where all the workers
eat chocolate every day."

Not only that, it's free.

Free chocolate! Yeah, mm!

I love it.

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

but they have smiles on their faces."

Wouldn't you?

Free chocolate all day long.

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

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

But we still gotta look at it critically.

Sorry, Catriona,
these people are happy,

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

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

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

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

maybe that's what's making them happy?

Sure, all these people in the factory
are happy.

But it might not be the chocolate.

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

So I think this fourth bit of evidence is
not really all that strong.

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

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

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

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

But of course, that's not
the right way to think about it.

She gave us four bits of evidence.

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

we've still got three left.

So if those first three bits of evidence
are good, and if they show at least

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

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

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

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

that we studied in the weeks
on inductive reasoning.

So, thank you very much, Catriona,

for submitting this wonderful video,
this wonderful argument.

We all learned from it
and we appreciate it.