5. Relevance
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Relevance
ƒ “Relevance,” you’ll recall is the second of
Govier’s ARG conditions. So, no surprise, it is
important to understand the idea of relevance
in order to evaluate arguments.
ƒ As Govier notes (172), however, the idea of
relevance is so basic to thinking and the
development of knowledge that it is difficult to
define.
Still, there are some things that we can
usefully say about it …
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Understanding Relevance
ƒ
Govier distinguishes three basic ideas about
relevance:
1. Positive Relevance
2. Negative Relevance
3. Irrelevance
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Positive Relevance
Statement A is positively relevant to another
statement B if and only if the truth of A
counts in favour of the truth of B. I.e., A
provides some evidence for B, or some
reason to believe that B is true.
Condition: If A is true (acceptable), then A
supplies some evidence or support for B.
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Example
1. University graduates have, on average, much higher
salaries than people who don’t go to university.
2. University graduates are more likely to be promoted.
3. University graduates are more likely to end up in
professional and managerial positions.
4. Getting a university education is a good way for an
individual to build a better economic future.
1, 2, and 3, are all positively relevant to 4.
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Negative Relevance
Statement A is negatively relevant to another
statement B if and only if the truth of A counts
against the truth of B.
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Example
1. Experts attribute a marked rise in childhood obesity
and adult onset diabetes to our increased consumption
of fast food.
2. Fast food can be part of a healthy diet.
1 is negatively relevant to 2.
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Irrelevance
Statement A is irrelevant to another
statement B is and only if it is neither
positively relevant nor negatively relevant to
B.
When there is irrelevance, there is no
relationship of logical support or logical
undermining between the two statements. A
does not provide a reason for B; nor does it
provide a reason against B.
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(Classic) Example
1. It’s new!
2. It’s improved!
The truth of 1 is irrelevant to the truth of 2.
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Example (Govier’s)
1. Natural catastrophes such as earthquakes are
beyond human control.
2. Human beings have no freedom of choice
concerning their actions.
1 is irrelevant to 2; the fact that some things
are beyond our control says nothing about
things that are under our control.
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Relevance and the ARG Conditions
ƒ If the premises of an argument considered
together are irrelevant or negatively relevant
to the conclusion, then that argument is not
cogent.
And, any time the premises of an argument
fail the R condition, the argument as whole
fails the G condition as well—irrelevant or
negatively relevant premises cannot provide
adequate grounds for any conclusion.
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Premises that seem to be irrelevant
ƒ Govier notes that sometimes premises which
seem to be irrelevant can be made relevant if
we assume one or more missing premises.
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Govier’s Example
1. Both our [Western] type of alphabet and our type of
numbers originate from the Middle East.
So,
2. Western civilization as a distinct entity does not exist.
At first glance, 1 appears to be entirely
irrelevant to 2, but can make it relevant by
supplying some missing premises that the
arguer may have intended …
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1. Both our [Western] type of alphabet and out type of
numbers originate from the Middle East.
3. The Middle East is not part of the West.
4. A civilization is a distinct entity only if all of its
important elements come from within its own area.
So,
2. Western civilization as a distinct entity does not exist.
3 and 4 make 1 relevant to 2, but only introducing
some possibly unacceptable premises; the argument no
longer fails R, but it may fail A.
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Another (Simpler) Example
1. Sheryl has brown eyes
Therefore,
2. Sheryl is a good hockey player.
1. Sheryl has brown eyes
3. People with brown eyes are good hockey players
Therefore,
2. Sheryl is a good hockey player.
By adding 3., we can make 1. relevant to 2., but only
at the cost of introducing an premise of doubtful
acceptability.
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“Expansive Reconstruction”
ƒ Some informal logicians maintain that it is (sometimes)
acceptable to supply a missing premise in order to
overcome R problems (Recall: the “principle of charity”)
ƒ Govier cautions. however:
1) Can we be sure that we are reconstructing the
argument and not supplying a new argument?
2) We may simply shift the problem from one ARG
condition to another (as in the previous examples).
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Non Sequiturs
ƒ Non sequitur < Latin “does not follow”
An irrelevant premise or any remark that
seems irrelevant or out of context.
(Reportive definition context: generally,
simply a mistake, not something that an
arguer does consciously).
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Red Herring
ƒ A distracting remark that is irrelevant to the
argument and leads an audience away from
the point at issue.
(Reportive definition context: sometimes
simply a mistake, sometimes a strategy
consciously in order to persuade).
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Example: A dialogue
A. Why are you not willing to support gun
control legislation? Don’t you have any
feelings for the thousands of lives that are
lost each year do to gun violence?
B. I don’t understand why people who get so
worked up people being killed by guns don’t
have the same feelings for the thousands of
unborn children whose lives are blotted out
each year. Isn’t the sanctity of life involved in
both issues? Why haven’t you supported our
anti-abortion legislation?
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Fallacies of Relevance
We’ve already encountered a few fallacies
(common mistakes in reasoning, of a sort
that people tend not to notice) in connection
with ambiguity and vagueness. (equivocation,
begging the question)
Govier now introduces several more:
1.
2.
3.
4.
5.
The Straw Man Fallacy
The Ad Hominem Fallacy
Guilt by Association
Fallacious appeals to Popularity
Fallacious appeals to Ignorance
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The Straw Man Fallacy
ƒ The straw man (or woman) fallacy is
committed when a person misrepresents an
argument, theory or claim, and then, on the
basis of the misrepresentation, claims to have
refuted the position that he has
misrepresented.
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Example: A dialogue
You say: “Christmas has become overcommercialized and depressing”
I say: “Why do you want to do away with
Christmas! It makes kids happy. It stimulates
the economy. Moreover, it is one of our great
Christian traditions and we must maintain our
traditions or society will crumble”
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Avoiding the Straw Man in Evaluating Arguments
ƒ The straw man fallacy involves
misrepresenting someone else’s position, so
perhaps the most straightforward way to avoid
the fallacy is to avoid tinkering with someone
else’s argument:
Stick to the argument as presented (if
available)
Avoid adding premises and/or rewording; if
you must do so (and sometimes we must)
check and re-check to make sure that your
interpretation is has a firm basis in what the
arguer actually says.
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The Ad Hominem Fallacy
ƒ Ad hominem < Latin “to the man” (as opposed
to the argument).
“To reason from premises about the
backgrounds, personalities, characters or
circumstances of people to substantive
conclusions about their arguments is to
commit the ad hominem fallacy unless the
premises are relevant to the conclusion
because it is about the person or depends on
acceptance of that person’s authority or
testimony.” (185-6)
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Reportive context
ƒ Ad hominem arguments are almost always
defective from a logical point of view. Yet they
are a common tactic in real-world debates
(especially legal and political debates).
Sadly, they are all-too-often practically
effective.
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A “Natural” Human Weakness?
ƒ A Govier points out, many a good idea has
been rejected because the person proposing it
didn’t belong to the “right” class or race or
gender or religion or ethnic group.
ƒ In logical terms, this sort of prejudice is not
simply unattractive or unethical it is flat out
mistaken: The characteristics of the person
offering the argument are one thing; the
merits of the argument are another.
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A Special Case of Ad Hominem: To Quoque
ƒ To quoque < Latin “you too”
E.g.:
Doctor (puffing on a cigarette): “Smoking is
damaging your health. You should quit now.”
You: “How can I believe you when you say
that? You smoke too!”
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Guilt by Association
The fallacy of guilt by association is committed
when a person or his or her views are
criticized on the basis a supposed link between
that person and a group or movement
believed to be disreputable.
E.g.,
“Voluntary euthanasia is wrong. Hitler and the
Nazis practiced it.”
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Fallacious Appeal to Popularity
ƒ Or, in logicians’ lingo: argumentum ad
populam
Examples:
“20,000 Elvis fans can’t be wrong”
“Everybody’s doing it”
“Isn’t that what most people think?”
“Everybody knows that X”
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Govier’s Definition
The appeal to popularity is a fallacy that
occurs when people seek to infer merit or
truth from popularity. It is known as the
fallacy of bandwagon jumping or, in the Latin,
ad populam.
The premise or premises of such an argument
indicate that some product or belief is popular.
… The conclusion of the argument is that you
should accept [the argument] because it is
popular.
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A Special Case: Fallacious Appeal to Tradition
ƒ A variation on the ad populam in which the audience is
asked to accept the merit or truth of some claim or
practice because that claim or practice is traditionally
accepted.
ƒ Many traditions are valuable. Possibly the health of a
community depends on maintaining at least some
traditions.
But traditions are not immune from rational criticism
just because they are traditions.
Consider: foot-binding, clitorodectomy
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Fallacious Appeals to Ignorance
ƒ
Or, in logicians’ lingo: argumentum ad
ignorantiam. An appeal to a lack of evidence
in support of some positive conclusion.
E.g.,
1. We don’t know that S is true
Therefore,
2. S is false
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Reportive Context: Argumentum ad ignorantiam
ƒ Especially common in connection with things
that some/most people think do not exist:
Extraterrestrial life, God, telepathy,
reincarnation, unicorns, WMDs …
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Rumsfeld:
There are things we know that we know.
These are the known unknowns—that is to
say, there are things that we know we don’t
know—but there are also unknown unknowns.
There are things we do not know we don’t
know. So when we do the best we can and
pull all this information, we then say well
that’s basically what we see as the situation,
there is really only the known knowns and the
known unknowns. And each year we discover
a few more of those unknown unknowns.
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ƒ From ignorance, Govier rightly says, we can
infer only lack of knowledge. We cannot infer
truth or falsity or probability or improbability
from the absence of evidence.
ƒ One exception: In an empirical investigation of
discoverable entities (“we should find Xs here,
according to our theory”), the absence of
evidence may rightly be taken as evidence of
the non-existence of those entities in the
context under investigation.
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Some Other, Related, Fallacies
ƒ Argumentum as misericordiam: Appeal to pity
Accept my conclusion or I’ll be sad, accept my
conclusion or I will suffer and/or be pitiable.
ƒ Argumentum ad baculum: Appeal to force
Accept my conclusion or you will suffer.
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