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 we are 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. 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 and 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 show that the argument is
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 suppressed premises, enough of them to make the argument valid. But that might
seem like cheating. I mean, you 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 is it that's 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 everyday 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. So, it's useful to fill out the argument with suppressed premises to
make sure it really is valid, because that brings those assumptions out in the open,
where we can assess whether or not they're true or 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
got to see every single footprint. So, the goal of bringing up the suppressed
premises is to let us trace exactly where the reasoning is 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 miss-steps or they are trying to hid something from
us by getting rid of one of their footsteps, so that's the point of bringing
up suppressed premises. To accomplish these goals is tricky. You have to find
suppressed premises that are just strong enough to make the argument valid but not
so strong that there gonna be implausible. Cuz you don't wanna ascribe all kinds of
suppressed premises to the person that they didn't really believe, and 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. We put this in
standard form this way. First premise: This box rattles wh en 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 in 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
we want to focus on here and ask whether that argument is valid. The argument is
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, I'll hear something.
So that's possible, and that shows that the argument's 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. Now the
argument looks like this. This box rattles when I shake it. The 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 suppressed premise is
that a box that contains a sweater doesn't rattle when shaken and together they are
suppose 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 conclusions false.
Without the suppressed premise we saw this might be 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 has 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 fal se.
So that's not a case where the premises are true and the conclusions 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 an argument
that's very bad, when the argument is not sound. What we want really is soundness.
So, that's why we need the next step, mainly, check the supressed 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. Cuz you don't want to claim
that the person giving the argument was assuming this falsehood, when the didn't
have to. So let's see if there's some way to qualify this suppressed 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. You could add
that. You 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 is 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? Well, 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 suppressed 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 s
aw 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. And 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 that this box doesn't contain a sweater, cuz 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 your argument's not valid, we've
got to go back to that other step and add another suppressed premise. Remember how I
told you how these different steps within this stage work in tandem and what's
happening is you've got to check it for validity, add a suppressed premise,
recheck for validity, maybe add another suppressed premise, and that's what we're
doing now. So what kind of suppressed premised can we add. Well, we could add my
wife is 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 could make that a little
more explicit by making the suppressed premise something like this. If this box
contains a sweater, then it only contains 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 that rattles when shaken. So this box does not contain a
sweater. Now we have an argument that's valid. And the suppressed premises are
true, at least given our life's not a trickster, which she's not, I assure you.
And it looks like we have a sound rec onstruction, 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 talking 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 through 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, add suppressed premises that make it valid.
Check them for truth. If they're not true, you qualify them, and then you go back and
see whether that qualification made the argument not valid anymore. And 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 twelfth, 1849. Therefore, Charles Darwin also turned 40 on February twelfth,
1849. Now, is that argument valid? No chance. Of course it's possible for the
premise to be true and the conclus ion 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 twelfth, 1809. So
now, we've filled out the argument. Abraham Lincoln turned 40 on February
twelfth, 1849. Abraham Lincoln and Charles Darwin were born on the same day,
therefore Charles Darwin also turned 40 on February twelfth, 1849. Now is the
argument valid? No. It's still not valid. Cuz Darwin might have died before 1849. So
we have to add another suppressed premise. Mainly, that both Abraham Lincoln and
Charles Darwin lived beyond 40. So now we have a fuller argument. Abraham Lincoln
turned 40 on February twelfth, 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 twelve, 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 is that you ought to obey her. Well, is
that argument valid? No way cause 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 therefore
you ought to obey her, but of course that a supressed premise you ought to obey your
mother is questionable because maybe she was abusive or stupid. So let's add
another supressed premise that your mother was not abusive or stupid, of course we a
lso 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. An notice that here, we
added a moral premise about the 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 to go to
synagogue. Well, that's clearly not valid. One suppressed premise is that 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,
mainly 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 it's the
Sabbath, to the conclusion, that you ought to go to synagogue. And 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 someone
who gave the original argument. And anybody who says it's the Sabbath, so you
ought to go to synagogue, seems to be assuming 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 linguistic suppressed premises. Jen and Bob are first cousins, therefore
they share a grandparent. Now, in order to understand that argument, you have to know
that first cousins always share a grandparent. That just follows from the
definition of what a first cousin is. But i t's not quite so obvious, is that
biological sisters are female. And so, there's even more need to bring out that
linguistics 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 grandparent. 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
linguistics suppressed premise. So it's worth doing that. Shh. Here's a trick.
Don't tell anybody. Okay? It's just between me and you. You can 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 start making 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 adding
suppressed premises which is to understand the pathway of reasoning. So you can do
that. It's a trick. It makes that 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 politic debates, politician 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 those little details. But
sometimes politicia ns abuse suppressed premises. They take things for granted
that they shouldn't be taking for granted. 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, 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 the suppressed premise that if you've read
those studies you'ld 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 will be questionable, and that's 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
finished reconstruction. Yipee, 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,
you've got to 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 couldn't come up with a sound
reconstruction because we just weren't imaginative enough, or try hard enough.
Still, if we try really long an hard, and charitably interpret the a rgument 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 is true. And so, this method of reconstruction can lead us
either to the belief that the argument is sound, because we found the sound
reconstruction, or to the conclusion is not sound, because we tried long and hard
to find a sound reconstruction that 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 is the argument 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 is sound or not.