Critical Thinking Fundamentals: Introduction to Critical Thinking

Geoff Pynn (Northern Illinois University) gets you started on the critical thinking journey. He tells you what critical thinking is, what an argument is, and what the difference between a deductive and an ampliative argument is.

(intro music)

I'm Geoff Pynn. I teach at

Northern Illinois University,

and this is an introduction
to critical thinking.

In this lesson, we're gonna
talk about three things.

First, what is critical thinking?

Second, what is an argument?

And third, what's the difference between

deductive and ampliative arguments?

Okay, so what is critical thinking?

Well, fundamentally, critical thinking

is about making sure that you have

good reasons for your beliefs.

What does that mean?

So suppose that you and your friend

are talking about who's
gonna be at tonight's party.

And she says to you, quite confidently,

"Monty won't be at the party."

You're not sure whether
or not to believe her,

so it would be natural
for you to follow up

by asking, "Why do you think so?"

And there are a lot of different things

that she might say in response.

We're gonna talk about three

possible answers she could give.

First, she might say, "I can't stand him,

and I want to have a good time."

Second, she might say,
"Well, he's really shy,

and he rarely goes to parties."

And third, she might say,

"He's in Beijing, and it's impossible

to get here from
Beijing in an afternoon."

The first response that she gives you

does not give you a good reason to believe

that Monty won't be at the party.

The second reason,
though, is a good reason

to believe that Monty
won't be at the party.

If he's really shy and
rarely goes to parties,

then it's probable that he
won't be at tonight's party.

Similarly, the third reason
also gives you a good

reason to believe that
Monty won't be at the party.

If he's in Beijing, and
it's impossible to get here

from Beijing in an afternoon,
then it's guaranteed

that he won't be at the party.

And when you notice things like that,

when you distinguish between good

and bad reasons for believing something,

you're exercising your
critical thinking skills.

So critical thinking is making sure

we have good reasons for our beliefs,

and so one of the essential
skills that you learn

when you're studying
critical thinking is how

to distinguish good reasons
for believing something

from bad reasons for believing something.

Now, it's worth saying something about

how I'm using the term "good" here.

I'm not using it to indicate anything

having to do with morality or ethics.

So it's not morally right or morally good

to believe something on
the basis of good reasons.

Similarly, it's not morally
wrong, or evil, or wicked

to believe something on
the basis of a bad reason.

Rather, here, what it is to
say that a reason is good

is closely tied to the notion of truth.

So a good reason for a belief is one

that makes it probable, that is, it's one

that makes the belief likely to be true.

The very best reasons for a belief

make it certain, they guarantee it.

So why does this matter?

Well, the reason that critical thinking

is important is because,
since we're rational,

we want our beliefs to be true.

Rational people want to have true beliefs,

and they want not to have false beliefs.

And the best way to be
rational in this way

is to form beliefs only when you

find good reasons for them.

Okay, that leads us to
our second question:

What is an argument?

Well, an argument is a set
of statements that together

comprise a reason for a further statement.

So, for example, we can consider one

of your friend's responses
before as an argument.

She's given you two statements,

"Monty's really shy" and
"Monty rarely goes to parties,"

which together comprise
a reason for believing

that Monty won't be at the party.

The statements that are the reason,

we call the argument's premises.

So "Monty's really shy" is premise one,

"Monty rarely goes to
parties" is premise two,

and the statement that
those premises give you

reason to believe, we call
the argument's conclusion.

A good argument is one
in which the premises

give you a good reason for
the conclusion, that is,

the premises make the
conclusion likely to be true.

In that case, we say that the argument

supports the conclusion.

Good arguments support their conclusions,

and bad arguments don't
support their conclusions.

So a key part of critical
thinking is learning

to evaluate arguments to determine

whether or not they're good or bad,

that is, whether or not their premises

support their conclusions.

The red argument is the first response

that she gave, two premises,

"I can't stand Monty" and "I
want to have a good time."

And the conclusion is "Monty
won't be at the party."

And the third argument,
which we'll put in purple,

consisted also of two premises,

"Monty's in Beijing" and
"He can't get from Beijing

to the party in time, so
he won't be at the party."

Now, as I indicated
before, the first argument

is not good, while the
purple argument is good.

And here I can explain a
little bit more about why.

If you consider what the
red argument's premises say,

that your friend can't stand Monty,

and she wants to have a good time,

and think about their relationship

to the conclusion of the argument,

you'll see that those
statements don't make

that conclusion any
more likely to be true.

The fact that your
friend can't stand Monty

and wants to have a good
time doesn't do anything

to make it more likely
that Monty won't be there.

It's simply unrelated to the conclusion.

In the purple argument,
though, the premises,

if they're true, they guarantee
the conclusion is true.

So they make it very probable.

The truth of the premises
guarantees the truth

of the conclusion, and so
in the purple argument,

the premises do support the conclusion.

Now, it's worth pointing
out that the red argument,

though it's bad as it
stands, could be made

a good argument with the addition

of some background premise.

So, for example, if you found out

that your friend was
the person who decided

who was going to be invited to the party,

then the fact that she can't stand Monty

and wants to have a good time

would give you a good reason to believe

that Monty won't be at the party,

because it would give you reason

to believe that she didn't invite him.

But as it stands, the
argument is not good.

Those two premises
considered in themselves

give you no reason to believe

that Monty won't be at the party.

Okay, our last topic is to distinguish

two different types of arguments.

So I'm gonna put up here, on the left,

the orange argument, which is the

second response that your friend gave,

"Monty's really shy" and
"He rarely goes to parties."

On the right we'll put
the purple argument,

"Monty's in Beijing" and

"He can't get from Beijing
to the party in time."

Both of them have the same conclusion,

"Monty won't be at the party."

Now, as I said before, both of these

are good arguments, they both do

give you reason to believe the conclusion,

i.e., both of them have premises

which support the conclusion,

but there's an important difference

between the two arguments
that I want to point out.

If you consider the purple argument,

and think about what those premises say,

you'll notice that if
those premises are true,

if Monty's in Beijing,
and can't get from Beijing

to the party in time, then it must be true

that Monty won't be at the party.

Those premises guarantee the conclusion.

In such an argument, where the premises

guarantee the truth of the conclusion,

we call the argument deductive.

In a deductive argument,
given the premises,

the conclusion must be true.

Just thinking about the information

in the premises in a deductive argument

gives you all you need
to deduce the conclusion.

If you look at the
orange argument, though,

you'll notice that that's not the case.

In the orange argument,
even if those premises

are true, the conclusion
might still be false.

Even given that Monty is really shy

and rarely goes to parties,
it's still possible

that he'll get over
his shyness and suspend

his policy of rarely going to parties,

and unexpectedly show up.

It's unlikely, but it's possible.

So the truth of the premises
in the orange argument

does not guarantee the
truth of the conclusion.

Arguments like this, we call ampliative.

In an ampliative argument,
the truth of the premises

makes the conclusion probable
but doesn't guarantee it.

Now, as I said, both of
the arguments are good.

Ampliative arguments can often be

very good arguments,
they're just not deductive.

The premises don't guarantee
the truth of the conclusion.

Now, when you're evaluating an argument,

it can be important to know whether or not

the argument is supposed to be deductive

or supposed to be merely ampliative.

If an argument is
supposed to be deductive,

but careful consideration of the argument

reveals that in fact the premises

don't guarantee the
truth of the conclusion,

if the conclusion could
be false even though

the premises are true,
that's often a good reason

to reject the argument as a bad argument.

Whereas in an ampliative argument,

to notice that the truth of the premises

doesn't guarantee the
truth of the conclusion,

is simply to notice that
it's an ampliative argument.

If you were to object
to the orange argument

by pointing out that,
still, the conclusion

could be false, you'd
really be missing the point.

In an ampliative argument,
it's taken for granted

that the conclusion is not
guaranteed by the premises.

Rather, what an ampliative
argument is doing

is giving you reasons to think

that the conclusion is probable.

So knowing what type of
argument an argument is

is essential to knowing which tools to use

to evaluate whether or
not it's a good argument.

And we'll talk quite a bit more

about different tools for
evaluating both ampliative

and deductive arguments in future lessons.

Okay, so summing up this lesson.

Critical thinking is making sure

that we have good reasons for our beliefs,

where we understand a good reason as one

that makes the belief
probable, or likely to be true.

An argument is a set of statements,

which we call premises,
that together comprise

a reason for another statement,

which we call the argument's conclusion.

And in a good argument, the premises

support their conclusions, that is,

the premises give you a
good reason for believing

the conclusion, because
they make it probable.

A deductive argument is
one where the conclusion

is guaranteed by the premises.
If the premises are true,

then the conclusion must be true.

An ampliative argument
is one where the premises

don't guarantee the conclusion,

but they do make it probable.

So they can still provide you

with good reason for
believing the conclusion.

Okay, so that ends this
introductory lesson.