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Similarity and Difference
Rational inquiry is often initiated by the detection of
an unusual similarity or difference. Reasoning that depends on reasons that make explicit
claims about similarity and difference is called analogical reasoning.
Two analogical arguments can be distilled from the following example.
Example 5
- Rachel:
Dad, why does Jessie get to go out tonight? He didn't finish his
homework this week either.
- Dad: I
know that, but Jessie happens to be getting straight A's and he didn't
finish his homework because he was helping me fix the car. You just spent
too much time on the phone. And Jessie and Mike
aren't just going out tonight, they're going to help with the homecoming float.
- Rachel: But I want to help with the
float, too!
- Dad: Well, that's
interesting. That's not what you wanted to do before I grounded you.
Your mother tells me you were going to the movies with Vinny.
- Rachel: It wasn't Vinny and he's not
vile! See, you're not grounding me because I didn't do my homework,
you're grounding me because you thought I was going out with Vinny!
The respective principles in the above rationales are
typical variations on the following two analogical principles.
- Principle of Similarity: If x and y are the
same, then x and y should be (or are) treated the same.
- Principle of Difference: If x and y are
different, then x and y should be (or are) treated differently.
These principles sound sensible, and when the
terms "same" and "different" are interpreted very strongly (e.g., if "same"
means "identical" or "sharing every single property to the same degree"; and
"different" means "absolutely distinct" or "having absolutely no properties in
common") they have some obviously sound applications.
For example, if you have the job of grading apples for
quality and you see two apples that seem to be identical in every respect they
should get the same grade. On the other hand, if you are just looking for
an apple to eat and you are given these two apples to choose from, so that
there is no legitimate to prefer one to the other, you still aren't going to
treat them totally the same, since you are going to eat only one of them.
Similarly, if your job is to separate apples from
oranges, then if you see an apple and an orange you will treat them differently
by putting the apple in the apple box and the orange orange box. But, if
you are hungry for an apple and an orange, then you might eat them both, thereby
violating the principle of difference which instruct you to treat them
differently.
In ordinary contexts the situation gets quite a bit
murkier because "same" and "different" are usually used to mean "having some of
the same properties" or "having some different properties." And the
problem here is that just about any two objects in the world have some similar
properties and some of the same properties. Your brain and a marshmallow
are similar in that they both contain a lot of carbon and they will both fit in
inside a large jack-o-lantern. On the other hand, they are different in
that marshmallows can't solve logic problems and your brain consumes more calories.
All this means that analogical reasoning is often very
unreliable no matter how careful you are, but to give it the best chance of
being useful we need to be sure that claims about similarity and difference are
appropriate to the context of comparison. In the example above, it's easy
to see that Rachel and Dad differ, not so much about the actual similarities and
differences, but about which similarities and differences are strongest
and most relevant in the given
context to the conclusion being drawn. Rachel claims that the
similarity between Jessie and Rachel is strongest and most relevant, and that
is why Jessie and Rachel should be treated the same. Dad claims that the
differences between Jessie and Rachel are strongest and most relevant in this context, and
that is why they should be treated differently.
This, of course, just raises the further question how
one establishes strength and relevance in a context. Here the matter is pretty easily
resolved. The differences between Jessie and Rachel are relevant to
differential grounding because grounding in this context is ultimately for the
purpose of behavior modification, and Rachel's behavior is clearly in greater
need of modification than Jessie's. The differences are stronger, because So Dad appears to be right this time.
But things might have been different. If, for example, there had been an
explicit household rule that "If child x doesn't do x's homework, then x
is grounded for the following weekend," then Rachel's similarity really should
have carried the day. Even though the rule is still ultimately about
behavior modification, another issue would have had even greater relevance, and
that is logical consistency and respect for the rule of law. (Relevance and
Logical Consistency will be treated in greater detail below.) This
discussion lead us to codify the following two errors.
Questionable Analogy (Weak Comparison)
- Basing a conclusion on an alleged similarity between two or more things
when it is not clear that the similarity in question is (a) sufficiently
strong or (b) sufficiently relevant to the context to provide adequate
support for conclusion.
MOI: Explicitly identify the similarity in question
and identify why you think it is insufficiently strong or insufficiently
relevant to the context to warrant the conclusion.
Distinction without a difference (Weak Distinction)
- Basing a conclusion on an alleged distinction between two or more
things when it is not clear that the distinction in question is (a)
sufficiently strong or (b) sufficiently relevant to the context to provide
adequate support the conclusion.
MOI: Explicitly identify the distinction in
question and identify why you think it is insufficiently strong or
insufficiently relevant to the context to adequately support the conclusion.
These errors are obviously very similar in some ways,
but their differences are very strong and very relevant to this context!
Example 1
- Fletch: I don't care who wins the election. All politicians
are the same. They're all liars and crooks.
Identification: This is a weak comparison. The
similarity is
relevant to the context, but not particularly strong. Even if it were true that
all politicians are the same in the sense of being liars and crooks, some liars
and crooks may be better or worse politicians than other liars and crooks.
For example, both Richard Nixon and Bill Clinton apparently lied to congress and
broke the law. But they were not equally good or bad presidents because of
this.
Example 2
- Amanda: Ash, I don't know how you can keep talking on the cell
phone while you're driving when you know how dangerous it is. It kills
more people than drunk driving. You're basically a murder waiting to happen.
- Ashley: I know, but it really isn't that dangerous. The reason
it kills that many more people is because there's a lot more cell phone
users than drunk drivers. Every one who drives rather than walks is a
murder waiting to happen if you want to think that way. Besides, I use a
hands free cell phone.
- Amanda: You still shouldn't do it. That study we read said
that there's no difference between hand-held sets and hand free sets.
- Ashley: Well, that can't be right. It's just common sense that
a hands free is safer. After all, you've got both hands on the wheel.
I know that I am very much in control.
Identification
This is a weak distinction. Ashley makes
a distinction between hands free cell phones and
hand held cell phones with respect to safety. This is a relevant
difference, but it is weak since there is
evidence against it, and the evidence she gives in support of her view is just
her own subjective feeling of safety.
It's worth noting that Ashley's first
point is actually quite legitimate. It's not nearly as dangerous for a
single individual to talk on the cell phone while driving as it is to be
intoxicated while driving, and that seems to be the relevant context for
individual decision making. But Ashley does makes a questionable
distinction between the two kinds of cell phones. She is rejecting the
data that show that there is no measurable difference between the two types of
cell phone as it relates to traffic accidents simply because she feels it's
wrong.
Example 3
- Klaus: You know, I used to really think that
being gay was totally perverted and wrong. But I'm majoring
in biology now, and I'm getting like this whole different perspective.
I've been reading how common homosexual behavior is in all sorts of
other species. So I'm really starting to see that homosexuality is
just a totally natural phenomenon, and that we shouldn't be so judgmental
about it.
Identification:
Weak Comparison. Klaus compares homosexuality in
humans to homosexuality in other animals, arguing that since homosexuality isn't
wrong in animals, it isn't wrong in people either. This relies on the
assumption that human homosexual behavior is like the homosexual behavior of
other species, as the rational below demonstrates:
The two behaviors, while physically similar, are not similar in a way that is
relevant to drawing moral conclusions. This is because the behavior of non
human animals is not subject to moral evaluation.
Example 4
- Fayanne: You know, I just voted and
rather than feeling good about it, I almost wanted to cry. There were these people in line who obviously had no idea what
they were doing. The whole time I'm thinking, my vote counts the same
as these idiots?
- Gabriela: Oh God, totally. I don't even get why people like
that should have the right to vote. I think there should be some kind of
test you have to pass, like our driving test. Bad voters do just as much
harm as bad drivers, right? Why shouldn't they have to get a license to
vote, too?
Identification: Weak Comparison. Gabriela argues
that people should not have the right to vote, rather that they should first
have to demonstrate competency by passing a test. Her reason for this is that
ignorant voting is like bad driving with respect to the degree of harm that can
be done, and a test is required of all prospective drivers. This is a
rather weak comparison because (a) a bad driver can do much more harm than a bad
voter and (b) the effectiveness and fairness of a driver competency test is more
easily established than the effectiveness and fairness of a voter competency
test.
After you examine a bunch of comparisons and
distinctions critically it's easy to start assuming that most comparisons and
criticisms are weak, which of course is not correct. The next two examples
provide an antidote to this tendency.
Example 5
- Seymour: Don't you think it's funny the
way people are all down on kids playing computers and video games because we
should be outside playing, but then when they hear about some kid who has
his nose in a book all the time and they're all "Oh, that's so
wonderful. I wish my Seymour would read more."
Identification:
This actually seems to be a strong comparison.
Seymour argues that reading and playing computer and video games are similar
insofar as they are both sedentary activities. It's possible that reading
has other benefits that video games doesn't, but that's not relevant to his
rather limited point.
Example 6
- Lars: Olaf, you know what you said about Gustav saying he was
going after my girl Gretchen? I went to kick his ass, and he said he
doesn't even know Gretchen.
- Olaf: So, what, he's calling me a liar?
- Lars: He said it wasn't true. He said he has his eye on
Hilda.
- Olaf: He's calling me a liar. Damn, now, I have to go kick his
ass.
- Lars: OK.
Identification: This is not a weak distinction. There is a
very important difference between lying and saying something that isn't true,
which is highly relevant to the context. Lying consists in willful deceit,
but one can say something false by accident.
Finally, it's important to realize that whether a
comparison or distinction is weak or strong is often a matter that can not
easily be decided, especially by people with limited knowledge of a subject.
In fact, analogies are quite often used to make people feel like they understand
things when they really don't.
Example 7
Senator Thrift: Most of my colleagues in the Senate
want the U.S. to borrow what will amount to trillions of dollars to bail out
major financial institutions and manufacturers. These are corporations who
largely created their own problems by running their businesses in irresponsible
ways. Every responsible working person knows that when times are tough you
do not borrow money to finance your spendthrift ways. What you do is
quit spending so damn much money. You tighten your belt, learn to live
with less, work harder, and pay off your debts. Why should the government
be any different?
Identification
This sounds like a compelling comparison, but the truth is
that the government is not like an individual household in this regard.
Government has longer time horizons,
a much greater ability to bear risk, and an almost unlimited access to capital.
More important, one of the legitimate functions of the government is to
stabilize the economy so that individual households can function. So while
it's true that the government has to pay attention to a lot of the same
financial issues that individual citizens do, it will sometimes be rational for
the government do things that would be irrational for an individual.
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