How to Understand Arguments Think Again: How to Reason and Argue Reasoning is important. This series of four short courses will teach you how to do it well. You will learn simple but vital rules to follow in thinking about any topic at all and common and tempting mistakes to avoid in reasoning. We will discuss how to identify, analyze, and evaluate arguments by other people (including politicians, used car salesmen, and teachers) and how to construct arguments of your own in order to help you decide what to believe or what to do. These skills will be useful in dealing with whatever matters most to you. Courses at a Glance: All four courses in this series are offered through sessions which run every four weeks. We suggest sticking to the weekly schedule to the best of your ability. If for whatever reason you fall behind, feel free to re-enroll in the next session.We also suggest that you start each course close to the beginning of a month in order to increase the number of peers in the discussion forums who are working on the same material as you are. While each course can be taken independently, we suggest you take the four courses in order. Course 1 - Think Again I: How to Understand Arguments Course 2 - Think Again II: How to Reason Deductively Course 3 - Think Again III: How to Reason Inductively Course 4 - Think Again IV: How to Avoid Fallacies About This Course in the Series: When is someone giving an argument instead of just yelling? Which parts of what they say contribute to the argument? Why are they arguing instead of fighting? What are arguments made of? What forms do they take? Think Again: How to Understand Arguments will answer these questions a more. In this course, you will learn what an argument is. The definition of argument will enable students to identify when speakers are giving arguments and when they are not. Next, we will learn how to break an argument into its essential parts, how to put them in order to reveal their connections, and how to fill in gaps in an argument. By the end of this course, students will be better able to understand and appreciate arguments that they and other people present. Suggested Readings: Students who want more detailed explanations or additional exercises or who want to explore these topics in more depth should consult Understanding Arguments: An Introduction to Informal Logic, Ninth Edition, Concise, Chapters 1-5, by Walter Sinnott-Armstrong and Robert Fogelin. Course Format: Each week will be divided into multiple video segments that can be viewed separately or in groups. There will be short ungraded quizzes after each segment (to check comprehension) and a longer graded quiz at the end of the course.
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來自 Duke University 的課程
Think Again I: How to Understand Arguments
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從本節課中
How to Reconstruct an Argument
<p><b>CONTENT</b>: This week’s material will teach you how to organize the parts of an argument in order to show how they fit into a structure of reasoning. The goal is to make the argument look as good as possible so that you can learn from it. We work through the main steps of reconstruction, including putting the premises and conclusion into a standard form, clarifying the premises and breaking them into parts, arranging the argument into stages or sub-arguments, adding suppressed premises where needed to make the argument valid, and assessing the argument for soundness. The lectures begin by defining the crucial notions of validity, soundness, and standard form. You will also learn to diagram alternative argument structures, including linear, branching, and joint structures. <p><b>LEARNING OUTCOMES</b>: By the end of this week’s material, you will be able to:<ul> <li>label assuring, guarding, discounting, and evaluative terms</li> <li>determine whether an argument is valid or sound</li> <li>complete arguments by adding suppressed premises</li> <li>reconstruct arguments by and series of arguments</li> <li>classify argument structures</li></ul><p><b>OPTIONAL READING</b>: If you want more examples or more detailed discussions of these topics, we recommend <em>Understanding Arguments, Ninth Edition</em>, Chapter 5.
與講師見面
Dr. Walter Sinnott-ArmstrongProfessor
Philosophy
Dr. Ram NetaProfessor
Philosophy
It's been a long and winding road, as the Beatles used to say.
But we're finally at the last stages of reconstructing arguments.
We've looked at stage one which is close analysis, stage two which is get down
to basics stage three, which is, sharpen edges.
Stage four, is organize parts.
And now we're doing stage five, which is, fill in gaps.
And we'll also get to stage six, which is, conclude.
Stage five really consists of four separate steps.
First, we need to assess the argument for validity.
Then we need to add suppressed premises. Enough of them to make it valid.
Then we need to assess those suppressed premises for truth or falsehood.
And then we need to qualify
the suppressed premises in order to make them true.
And the whole goal is to make the suppressed premises both
plausible for their truth and enough to make the argument valid.
So these steps within the stage really do work
in tandem together to try to make the argument good.
We already learned how to assess validity.
You simply ask is it possible for the
premises to be true and the conclusion false and
if so the argument is not valid and if not the argument is valid.
And the way you figure out whether it's possible is,
you try to tell a story or describe a situation.
And if you can describe a coherent situation where
the premises are true and the conclusion is false.
Then that shows that the argument's not really valid.
The main topic for today is what do you do.
When you assess the argument for validity and you
find out it's not valid.
And the answer is you add suppress premises
enough of them to make the argument valid.
Now that might seem like cheating.
I mean you'd start with an argument that's no good.
It's not valid and then you just throw in
some extra premises in order to make it valid.
Why isn't that just distorting the argument,
and making up something that wasn't there?
The answer,
is that it's not really bad.
And if it were bad, we'd all be in bad shape,
because in every day life, people always take things for granted.
They make assumptions.
We do it too.
And if we didn't, boy, our arguments would be really long and boring.
So there's something to be said in favor of suppressing premises,
at least the obvious ones that people really do take for granted,
but we can also get tricked.
People can suppress premises that really are questionable and they
just don't want us to see that they're making that assumption.
It is useful to fill out the argument with
suppressed premises to make sure it really is valid, because
that brings those assumptions out into the open were
we can access whether or not they're true of false.
Another reason to fill in suppressed
premises is to understand the argument better.
Because, if people suppress premises, then they're showing
us some of their footprints along the path, but,
if we really want to know the full path that
their reasoning followed, we've gotta see every single footprint.
So, the goal of bringing out the suppressed premises
is to let us trace exactly where their reasoning went.
From one step to another. So there are two goals.
One is to trace the full path every step, and the other goal is to see if there are
any missed steps or they're trying to hide something
from us by getting rid of one of their footsteps.
So, that's the point of bringing out surpressed premises.
To accomplish these goals is tricky.
You have to find suppress premises that are just strong enough
to make the argument valid but not so strong that they're going to
be implausible.
because you don't want to ascribe all kinds of suppressed premises to the person
that they didn't really believe and that
they didn't really need for their argument.
So it's kind of like Goldilocks and the Three Bears.
You want suppressed premises to be not too hot, and not too cold, but just right.
Here's an example from a previous lecture. My wife always gives me
either a sweater or a board game.
This box does not contain a sweater because it rattles.
When it's shaken.
So this time, she must have given me a board game.
And we put this in standard form, this way, first premise, this
box rattles when I shake it, and that shows you it doesn't contain a sweater.
Third, she always gives me either a sweater or a board game.
Conclusion, this time she must have given me a board game.
Now the first step of this argument is this
box rattles when I shake it and the conclusion there is it doesn't
contain a sweater, that's the part of the argument that we want to focus on here and
ask whether that argument is valid. No.
The argument's not valid, because it's possible for
the premise to be true and the conclusion false.
How can that happen? Well, my wife might be fooling me.
She might know that I expect either a sweater
or a board game, so she puts a sweater in
the box, and then she puts little rocks around the
outside, so when I shake it Well here is something.
So thats possible, and that shows the argument is not valid.
Well, how can we make the argument valid?
The question here is, can we add a suppressed premise
that will turn this invalid argument into a valid argument.
Here's one that will do the trick.
A box that contains a sweater. Doesn't rattle when shaken.
The other argument looks like this.
This box rattles when I shake it.
A box that contains a sweater doesn't rattle when shaken.
So this box doesn't contain a sweater.
The explicit premise, is that this box rattles when I shake it.
The suppress premise is that a box
that contains a sweater doesn't rattle when shaken,
and together they're supposed to support the
conclusion that this box doesn't contain a sweater,
but do they really support that conclusion?
Is the argument valid?
Well, it's valid only if there's no possibility that
the premises are true and the conclusion is false.
Without the suppressed premise, we saw that was possible, because my
wife might be fooling me and putting rocks around the sweater.
So let's see if that's going to ruin the validity of this argument.
No,
because, if the sweater's got rocks around it, so
it makes noise when I shake it, then, the
premise that says a box that contains a sweater
doesn't rattle when shaken, turns out to be false.
So that's not a case.
Where the premises are true and the conclusion's
false, because the premise is false in that case.
So, by adding this premise, we actually succeeded in making the argument valid.
The problem of course,
is that validity is not enough for a good argument, as we saw several lectures ago.
You can have a valid argument that's very bad when the argument's not sound.
What we want really is soundness.
So that's why we need the next step.
Namely, check the suppressed premises for truth.
Assess whether they're true or false, and if they're not true then
you need to qualify them in order to make them true, because you don't want to
claim that the person giving the argument was
assuming this falsehood when they didn't have to.
So let's see if there's some way to qualify
this surpresssed premise in order to make it true.
How can we qualify this premise to make it true?
How are we going to
do that, let me think, oh, what about that little word only?
We can add that.
We could say, a box that contains only a sweater doesn't rattle when shaken.
But the word only what exactly does that mean?
We need to clarify that. What exactly does the word only exclude?
It excludes something. That's the function of the word only.
But what does it exclude? Well.
It probably excludes other things that might make the rattling sound.
Like, if my wife put rocks in the box. So, we can clarify this premise by saying.
A box that contains only a sweater and not anything else
that might make a rattling sound when shaken, won't rattle when shaken.
Well is that premise true?
You might quibble about details but it's close enough for now.
What we need to do though is to go back and
determine whether when we put that suppress premise in, the argument's valid.
And the argument now looks like this. This box does rattle when shaken.
And a box doesn't rattle when shaken if it contains only
a sweater and not anything else that makes a rattling sound.
So this box doesn't contain a sweater.
Is that valid?
Well, no, for the same reason we saw
before, because my wife might be a trickster
who puts rocks around my sweater in the birthday present box, in order to fool me.
Then, the premises can be true, and the
conclusion, false.
It's possible that the first premise is true, this box rattles when I shake it.
The second premise is true, a box doesn't rattle when shaken if
it contains only a sweater and nothing else that makes a rattling sound.
But it's false.
If this box doesn't contain a sweater, because
it still does contain a sweater and it
contains a sweater in addition to those pesky
little rocks that make all that rattling noise.
Well if the argument's not valid we got to
back to that other step and add another suppressed premise.
Remember how I told you that these
different steps within this stage work in tandem.
and what's happening is, you gotta check it
for validity, add a suppressed premise, recheck it for
validity, maybe add another suppressed premise in.
That's what we're doing now.
So what kind of suppressed premise could we add?
Well, we could add, my wife's not a trickster.
But basically that amounts to, she wouldn't put rocks in
a birthday present with a sweater in order to fool me.
So we can make that a little more
explicit by making the suppressed premise something like this.
If this box
contains a sweater, then it contains only a sweater and it
doesn't include anything else that would make a rattling sound when shaken.
And now, we can stick that as an extra suppressed premise into the argument.
Now the argument looks like this.
This box, rattles when I shake it.
A box doesn't rattle when shaken if it contains only a
sweater and not anything else that makes a rattling noise when shaken.
If this box contains a sweater, then it contains only
a sweater, and doesn't contain anything else that rattles when shaken.
So this box does not contain a sweater.
Now we have an argument that's valid.
And the surpressed premises are true at least given that my wife's
not a trickster which she's not I assure you,
and it looks like we have a sound reconstruction.
Just what we were looking for.
Admittedly this argument is a lot longer and more convoluted than the original.
And that shows why people suppress premises instead
of talk in the way this argument goes.
And of course many people would be perfectly
well convinced by the original argument because, they
share the assumptions that are in the suppressed premises.
So why do we go to all the trouble
to go through this process and add the suppressed premises.
Remember, the reason is that we
want to understand the pathway between the premises
and conclusion, we want to understand how the reasoning works step by step by step.
And we want to do that because sometimes people are
going to include suppressed premises that aren't true and we
want to bring them out and make those assumptions explicit
so that we can assess them for truth and falsehood.
And when you're talking to somebody you trust, you might not have to do that.
And it's okay to suppress premises, but when you really want to know whether the
argument's any good that's when you want to
fill it out with the suppressed premises.
The point of going into detail on this
example, is to illustrate this stage of reconstruction you
want to assess the argument for validity, and suppress
premises that make it valid, check them for truth.
If they're not true, you qualify them.
Then you go back and see whether
that qualification made the argument not valid anymore.
And then you go back and forth, and
back and forth, until you've got a sound reconstruction.
The same steps are going to apply to all kinds of suppressed premises.
And sure enough, there are all kinds of suppressed premises.
So let's go through a few examples a lot more quickly in
order to show the variety of suppressed premises that are assumed in arguments.
Here's one example.
Abraham Lincoln turned 40 on February 12th,
1849. Therefore, Charles Darwin also turned
40 on February 12, 1849.
Now, is that argument valid? No chance.
Of course it's possible for the premise to be true and the conclusion false.
So we have to add a suppressed premise.
The suppressed premise is that Abraham Lincoln and
Charles Darwin were born on the same day, and
they were it happened to be February 12, 1809.
So now we've filled out the argument.
Abraham Lincoln turned 40 on February 12, 1849.
Abraham Lincoln and Charles Darwin were born on the same day.
Therefore, Charles Darwin also turned 40 on February 12, 1849.
Now is the
argument valid? No.
It's still not valid.
because Darwin might have died before 1849.
So we have to add another suppressed premise namely that both Abraham Lincoln
and Charles Darwin lived beyond 40. So now we have a fuller argument.
Abraham Lincoln turned 40 on February 12th 1849.
Abraham Lincoln and
Charles Darwin were born on the same day. Both of them lived beyond the age of 40.
Therefore, Charles Darwin also turned 40 on February 12, 1849.
Now the argument looks pretty good.
We had to have two suppressed premises, but we finally have a valid argument.
And what this shows is that sometimes the suppressed
premises are purely factual matters.
In this case, that they were born on the same day.
And that they both lived beyond 40.
So sometimes we have factual suppressed premises.
Here's another quick example.
You ought to obey her because she's your mother.
Here the premise is that she's your mother,
and the conclusion's, you ought to obey her.
Well, is that argument valid?
No way. because it's
possible that she's your mother, but it's false that you ought to obey her.
When could that happen?
Maybe she was like abusive, or stupid, or whatever.
Then maybe you ought not to obey her, even though she is your mother.
So, we have to add a premise. Namely, you ought to obey your mother.
Now, we can say she's your mother, you ought
to obey your mother, therefor you ought to obey her.
But of course, that is the suppressed premise you ought to
obey your mother is questionable because maybe she was abusive or stupid.
So let's add another suppressed premise that
your mother was not abusive or stupid.
Of course, we also have to qualify that moral premise that
you ought to obey your mother if she's not abusive or stupid.
And now the argument looks like this. She's your mother.
You ought to obey your mother if she's not abusive or stupid.
Your mother was not abusive or stupid, therefore you ought to obey her.
And notice that here, we added a moral premise about the that fact that
you ought to obey your mother under
certain conditions namely she's not abusive or stupid.
And the second premise is she was not abusive or stupid so we
have a moral premise and a factual premise.
Both being suppressed in the argument that you
ought to obey her, because she's your mother.
Here's another.
It's the Sabbath. So you ought go to the Synagogue.
Well, that's clearly not valid. Once suppressed premises you're Jewish.
The other suppressed premise is you haven't
been to Synagogue already today on this Sabbath.
And the third
suppressed premise is a religious norm namely
Jews ought to go to the Synagogue on
the Sabbath and you need that whole bunch of suppressed premises in order to get.
From the premise that is the Sabbath to
the conclusion that you ought to go to Synagogue.
Now of course all of those premises might be
questionable, some people would question them, some people would
deny them, but the point here is to figure out
what's being assumed by somebody who gave the original argument.
And anybody who says it's the Sabbath so you
ought to go to Synagogue, seems to be assuming
that you're Jewish, you haven't been already, and Jews
ought to go to the Synagogue on the Sabbath.
So what these suppressed premises do is
they bring out the assumptions that somebody
who gave that argument must have had in mind.
The last case is a little bit trickier.
It has to do with linguistics suppressed premises.
Janet and Bob are first cousins, therefore they share a grandparent.
Now, in order to understand that argument, we have
to know that first cousins always share a grandparent.
That just
follows from the definition of what a first cousin is.
But, it's not quite so obvious is that all biological sisters are female, and
so there's even more need to bring
out that linguistic suppressed premise in this case.
But it's still not necessary to make the argument valid.
It's just not possible that Janet and Bob.
Are first cousins, and they don't share, a grand parent.
Because the suppressed premise is purely linguistic, so it's necessarily true.
So, you can't possibly, be first cousins without sharing a grandparent.
Still, the point of bringing out linguistic suppressed premises is to
show every little step along the way the argument might be valid
without those suppressed linguistic premises but we won't understand
why it's valid and why the reasoning goes through unless we add the linguistic
suppressed premise. So it's worth doing that.
Sh, here's a trick. Don't tell anybody.
Okay? It's just between me and you.
You could always make any argument valid just by adding a suppressed
premise that says, if the premises are true then the conclusion is true.
But don't tell anybody because. If
people start doing that, and they make the argument valid that way, with that
suppressed premise, we're never going to understand the pathway of reasoning.
It makes the argument valid, but it doesn't serve the real purpose
of the unending suppressed premises, which is to understand the pathway of reasoning.
So you can do that, it's a trick.
It makes the argument valid, but it doesn't achieve
our goal because our goal is not just to
make the argument valid, it's to make the argument
valid so that we can understand the pathway of reasoning.
So, it's important to know that trick, but don't use it.
Unless you have to. The examples
so far have been pretty trivial, I admit it.
But the same points apply in
very important context, such as political debates.
Politicians can suppress premises in perfectly legitimate ways
they're just trying to save time and make their
arguments more efficient, maybe even sometimes clearer because you
don't have to add all of those little details.
But sometimes
politicians abuse suppressed premises.
They take things for granted that they shouldn't be taking for granted.
And here's an example.
A politician might argue, my opponent is soft on
crime because he's opposed to the death penalty, well,
that assumes as a suppressed premise that anyone who's
opposed to the death penalty must be soft on crime.
And if the politician were
to come
out and say that it would seem pretty questionable.
And that's probably why he suppresses it.
And then another politician might say, but my
opponent is in favor of the death penalty so
he must not have read all the recent
studies that show that the death penalty doesn't deter.
Well that argument assumes a suppressed premise that if you read those studies you
would be convinced by them and that the
only point of the death penalty is deterrence.
But the point is that politicians talking about extremely
important issues can take things for granted, that if
they were brought into the light of day would
be very questionable, and that is why they hide them.
So when you're listening to people give arguments on important
issues in your life, then you ought to be looking for
these suppressed premises and asking yourself whether or not you
really ought to be agreeing with them about that assumption.
Finally, we've finished
reconstruction. Yippee, right?
Oh, no, not quite. because there's one more stage.
And that stage is drawing a conclusion.
Of course, if we've come up with a
sound reconstruction then we know that the argument is
sound, and we know that the conclusion is
true, because every sound argument has a true conclusion.
But if we don't come up with a sound reconstruction, then what do
we say? Well we kind of ask whose fault is it.
It might be the fault of the argument maybe we couldn't come
up with a sound reconstruction because there just is no sound reconstruction.
But maybe we didn't come up with a sound reconstruction
because we just weren't imaginative enough or didn't try hard enough.
Still if we try really long and hard.
And charitably interpret the argument as
best we can to make it look as good as we can and we still can't
make it sound, then we've at least got
reason to believe that the argument's not sound.
Of course, that doesn't mean that the conclusion's not
true because unsound arguments can still have true conclusions.
But at least we know that this argument doesn't prove that the conclusion's true.
And so this method of reconstruction
can lead us either to the belief that the argument is sound because we found
a sound reconstruction or to the conclusion that the argument's not sound.
Because we tried long and hard to find a sound reconstruction and didn't.
But that's still not going to show us that the conclusion of the argument is false.
The point of reconstruction then is to
reach a conclusion on this issue of whether
the argument is sound or not.
And if we try our best, and do it as well as we can, and charitably, then
we can be justified in believing that the argument's sound or not.
