Transcript PHI 103 WED Reasoning and Argumentation

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Logic Slides 1
Propositions and Rules for Writing Short
Arguments
PHIL 211
Cosmos to Citizen
Dr. Mike Miller
Mount St. Mary’s College
Logic and Arguments
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Logic is all about arguments and reasoning well. In
particular, the study of logic teaches how to make
convincing arguments, to evaluate those of others,
and (if you deem it necessary) to defeat them.
Knowing these skills has always been important, for if you can reason well you can
protect yourself from those trying to dupe you. You can also greatly influence others
with your own persuasive arguments. And finally, you may even learn the truth –
the goal of many philosophers. So, what is an argument?
An Argument is a series of propositions
with a form or structure such that one
proposition (the conclusion) is affirmed
on the basis of the others (the premises).
What is a Proposition?
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Fine, that’s the definition of an argument. But what does it mean? And
what does proposition, conclusion and premise mean? Let’s find out . . .
A Proposition is the
meaning of a declarative
sentence and, as such, is
either true or false.
In other words, a proposition is a
declarative sentence that is either true or
false (that is, it has what is called a ‘truth
value’), but not both.
Somebody is almost always willing to
agree or disagree with every proposition,
even if they can’t prove it right or wrong.
So, if it is possible to claim that a given
sentence is true or false – even if it may be
silly to do so – then it’s probably a
proposition!
Are the following propositions?
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1) Plato is the greatest philosopher ever.
Yes. You may not know if this declarative sentence is true or false, but this
kind of sentence must be either true or false. So, this sentence is a proposition.
2) Close your notes and begin writing.
No. This is not a proposition because this sentence does not have a
truth value. That is, it is just a command. You may say ‘No, I don’t
want to,’ but you can’t logically respond ‘False’ or ‘True.’
3) Why must every person eventually die?
No. Questions are never propositions because they are not declarative
sentences.
4) Mount St. Mary’s is located in Texas.
Yes, because this declarative statement is either true or false. We all know
that the proposition is false, but someone in another part of the country may
not. What matters here is that the sentence must be either true or false.
Objective or Subjective?
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Every proposition is either objective or subjective.
A proposition is objective if it is true or false
independently of what anyone thinks, believes, or feels.
Objective propositions
are about things that can
generally be proven true
or false, even if you can’t
prove it yourself. For
example, look at the
following 4 propositions:
1+1=2
Objective, because it can be proven true.
1+1=3
Also objective because it can be proven false.
Christmas 2002 was on a Tuesday.
I don’t remember, but that doesn’t matter. The proposition is
objective.
Hydrogen has 4 atoms.
I don’t have a clue, but the proposition is still objective. I
trust someone can prove the answer.
* It is important to realize that objective propositions are not necessarily true.
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A proposition is subjective if it is not objective.
Subjective propositions are generally about what people think, believe or feel.
These propositions can’t be “proven” like objective claims. A proposition
remains subjective (even if someone is really sure it is true) if the proposition
isn’t something that can be proven by an independent and credible source.
The following propositions are all subjective:
I love to eat pizza. Fine, that may be true, but the truth of this proposition
depends fully upon your feelings. Your preferences may change tomorrow.
I think the Yankees are great. I strongly disagree (I think they are all jerks!),
but the strength of our opinions doesn’t make either proposition objective.
I believe in aliens. It may be an objective fact that aliens do or do not exist,
but the meaning of this sentence depends upon a belief, so the proposition
Sois. . .
subjective.
Are the following propositions objective or subjective?
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Emmitsburg was founded in 1785. Objective – historians disagree about when the town
was founded, but this is the kind of proposition that is true or false independent of anyone’s feeling,
thoughts or beliefs. Therefore, the proposition is objective.
Britney Spears is ugly.
Subjective. Is there one universal
standard of beauty? It varies from one person to another. So this
proposition is subjective.
Britney Spears is beautiful. Still subjective.
John said Britney Spears is ugly. Objective, because the truth of the proposition (whether
John really said what he said) is not dependent upon any opinion, belief or thought. Did he say
Britney is ugly or not? Don’t know? Your ignorance doesn’t change anything. It’s still objective.
Today is Friday.
Objective, because the sentence is true or false independently of what day
of the week you think it is.
God Exists.
Wow, this is a tough one. Some people would say objective because they believe
God’s existence can be proven. Others will say subjective because people either choose to believe
God exists or not. This example just shows that not everything – even in logic – is always clear cut.
NB: Please note that the issue separating objective and subjective propositions is not whether a proposition is true or
false, but if the meaning of the proposition is dependent upon feelings, beliefs or thoughts and not ‘independent’
verification. Also, please note that subjective claims can be true or false.
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OK, you now know what a proposition is, but what is an argument?
Our Logic Handout defines an argument as a series of
propositions with a form or structure that one proposition (the
conclusion) is affirmed on the basis of the others (the premises).
According to Anthony Weston, “to give an argument” means to
offer a set of reasons or evidence in support of a conclusion.
Given these definitions it should remain obvious that before you can understand
the point of any argument you must first determine which proposition is being
supported and which propositions are doing the support. Likewise, when you
are writing arguments you should follow Weston’s first rule in A Rulebook for
Arguments (p. 1-9) . . .
Rule 1: Distinguish premise and conclusion.
Premise and Conclusion
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Every argument contains a conclusion and at least one premise.
A Premise is a proposition on whose
basis another proposition is affirmed.
Every time this semester I go to Patriot Hall
after my 11:00 class they never have french
fries. They will not have french fries today
either.
A Conclusion is a proposition affirmed
on the basis of other propositions.
The person making the argument above is trying to convince us that the dining hall will not have
french fries because they were not available when he wanted them in the past. The reasons why
you should believe something are the premises. What you should believe is the conclusion.
Indicator Words
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An indicator word is a word or phrase added to a proposition that
helps make clear the role the proposition plays in the argument.
A conclusion indicator tells us which proposition is the conclusion.
A premise indicator tells us which proposition is the premise.
Common conclusion indicators:
Common premise indicators:
Therefore . . .
Since . . .
Hence . . .
Because . . .
So . . .
For . . .
Thus . . .
In as much as . . .
Consequently . . .
Given that . . .
It follows that . . .
It follows from . . .
See the chart on Page 7 of the logic handout for more indicator words.
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In order to make your arguments convincing, you need to make
the argument as clear as possible. One of the most important
rules to follow is . . .
Rule 2: Present your ideas in natural order
Generally, in a short argument either the premises come first and
then the conclusion, or the argument starts with the conclusion
and the premises follow. Both forms are acceptable.
Make use of premise and conclusion indicators to highlight to
your reader what you are arguing. Without these indicator words
your argument is often much harder to understand.
Underline the conclusion in the following arguments:
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Aristotle
hehe
was
upset
that
Plato
Aristotleleft
leftPlato’s
Plato’sAcademy
Academyinin410
410BC
BCbecause
because
was
upset
that
Plato
did not leave the school in his charge. (Notice the premise indicator in blue.)
Given that
Given
thatthose
thosethat
thatwho
whodo
dotheir
theirhome
homework
workget
getbetter
bettergrades
gradesand
and
better grades usually means a higher paying job, it follows that
thatyou
you
should
alwaysdo
doyour
yourhomework.
homework. (Once again, indicators make it
should always
easy.)
President
President Clinton
Clinton was
was born
born in
in Michigan.
Michigan. All
All people
people from
from Michigan
Michigan have
have “Buzz”
“Buzz” as
as their
their
middle
Clinton’s
middle
name
is Buzz.
middle name.
name. Therefore,
Therefore,President
President
Clinton’s
middle
name
is Buzz.
Note: this is an argument, even though both of the premises and the conclusion are false.
Arguments don’t have to be ‘good’ to be arguments. Bad arguments are still arguments. As long as
someone intends to support one proposition with another – you have an argument.
Over 1,000 people in MD receive burns on their body each year because
they misuse lighter fluid. Burns are very painful and leave ugly scars.
All of these injuries can be avoided. Always
Always follow
follow safety
safetyrules
ruleswhen
when
using
using lighter
lighterfluid.
fluid.
Even though the first sentence is a very brief argument it is not the conclusion of the
entire paragraph because the first three sentences all support the last sentence.
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Even if your premises do give reasons why your conclusion is true, your
conclusion will probably not be accepted if your premises are implausible. So, . . .
Rule 3: Start with reliable premises
Consider the following argument:
Since all children love to eat chocolate, Lucy should make
chocolate cake for Billy’s 7 year old birthday party.
Is the premise reliable? No. Not every kid I know loves to eat Chocolate.
Since this premise claims too much it’s unreliable and the argument is bad.
Although the following argument is very similar, it is more successful because
the premise is more reliable.
Since most children like chocolate, Lucy should make chocolate cake for
Billy’s 7 year old birthday party.
The argument is still not perfect, but it is better.
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It is very important to realize that just because something
sounds plausible, it doesn’t make it true.
Plausibility does not equal truth!
Did you know that the government is hiding information about
UFO’s and alien life forms in Area 51 in Groom Lake, Nevada?
Think about it – they let no one in Area 51, they refuse to answer
questions about it, and they are now increasing security. Besides,
people have seen things that they deny – for obvious reasons!
OK, it’s possible that aliens are in Area 51, but I don’t
think it’s plausible. So, I won’t believe it is true.
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When writing arguments always follow . . .
Rule 4: Be concrete and concise
Long complex sentences and wordy expressions will often lose your
readers. As one of my favorite teachers in college often said, ‘Omit
needless words! Omit needless words! Omit needless words!’
Vague expressions also confuse your readers.
A sentence is too vague when it is
unclear what the speaker intended.
That is, when you hear a sentence that is too vague, you end up asking, “what do
you mean?” Without additional explanation, you simply can’t understand what the
person is saying so you can’t determine if the proposition is true or false.
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Why are the following sentences too vague?
Lasagna is the best. The best what? Dinner? Italian dish?
Let’s interview an old person. What do you mean by old?
Tall people need help. Who’s tall? What kind of help?
Ferrets are wonderful. Wonderful at what? Digging?
Running? Singing?
Note: The issue isn’t whether a sentence is vague, but whether
it’s too vague, given the context, for us to be justified in saying it
has a truth value.
Spin Doctors at Work
Arguments that distort or mock your claims or those of others
are to be avoided. Language that is used to do this is intended
to sway the emotions and is called ‘loaded.’ So, always . . .
Rule 5: Avoid loaded language
When you give an argument, you should strive to stick to the
evidence. If you resort to playing games with words and
phrases to make your point rather than the reasons themselves,
you really are not making an argument. You are trying to
deceive your reader.
There are several ways to deceive with loaded language in the
premises or conclusions of arguments . . .
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Unfortunately, we often try to make some claims or arguments
sound better or worse than they really are.
A Euphemism is a word or phrase that makes
something sound better than its neutral description.
Warden: Bring our guests to the pacification center.
Better: take the prisoners
to their jail cells.
Spy Director: I sent an insurgent eradicator to terminate a soft target.
Why not say it like it is?: I sent an assassin to kill a rebel.
It is not always clear if some words or phrases are deceptive.
President Reagan: ‘I sent the troops to rescue the people of Granada.’
Did Reagan use the word ‘rescue’ to make an invasion of a foreign nation
sound ‘better’ than it was? Or, was it really a rescue operation?
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The opposite of an Euphemism is called a Dysphemism
A Dysphemism is a word or phrase that makes
something sound worse than its neutral description.
John put a pollen-producing, flower
bee-attracting organism on your desk.
earned the most
Biff monopolized
the votes to become class president
Hey, your ball spouse
and chain is on the phone and wants to talk to you.
A lie usually is not considered a euphemism or a dysphemism – unless it uses an
emotionally ‘charged’ word inplace of a neutral one.
Can you replace each Dysphemism with a more neutral word?
And not every euphemism is bad. For example, many consider it more polite to
say that a loved one ‘passed away’ than died. It is important to recognize that in
this situation you are not tying to deceive anyone.
Euphemisms and dysphemisms are always problems, however, when they ask you
to accept a dubious concealed claim.
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A Down-player is a word or phrase that
minimizes the significance of a claim.
But your Honor, I only shot him in the head once!
Our new Dishwasher is just $699.99.
Qualifier words, italics, and even the tone of our voice are all
used to downplay a claim. Qualifiers are often called weasel
words because they suck most of the content out of statements.
High debt could be one of the possible causes of the recession.
Peer pressure arguably is the greatest influence on young kids.
Janice Smith has won one of our two $1,333,333 prizes!*
*If she returns the grand prize entry, we will be pleased to announce that . . . .
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An Up-player is a word or phrase that
exaggerates the significance of a claim.
Good news! You get to clean the bathrooms today.
Doctor to patient: You have what few men ever have – a
chance to put things in order before you leave this world.
An extreme version of an Up-player is called an hyperbole.
My daughter’s goal in the closing minute of her kindergarten
soccer game had to be the greatest moment in sports history!
Come and get your mile-high ice cream cones!
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If you do not use consistent terms in your premises and conclusion
you have violated . . .
Rule 6: Use Consistent Terms
Arguments depend upon connections between the premises and the
conclusion. If your reader can’t easily see the connection between
the two parts he or she will likely not understand your argument.
Even though you can legitimately call one thing by several names,
don’t do it if doing so confuses your audience.
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When arguments slide from one meaning of a term to another in order to make
their case they have broken . . .
Rule 7: Stick to one meaning for each term.
A proposition suffers from equivocation if there
are at least two clear ways to understand it.
Equivocation is a problem because two very different but ‘correct’ meanings can be
taken from the sentence. Although one meaning may be silly, it is still a possible
meaning. For example:
Do you ‘catch’ the two possible
• Dogs smell better than horses.
meanings in each sentence?
• I shot an elephant in my pajamas.
Which meaning is the true meaning?
Are you sure?
• I went to the bank to get money.
• Biff hit the waiter with the glasses.
Although we can tolerate some vagueness in arguments, we can never tolerate
equivocation in reasoning.
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Here’s a example of an argument that breaks the rule against
equivocation:
Peggy said she has a frog in her throat. Frogs live on lily pads.
Therefore, Peggy must have a lily pad in her throat as well.
The example above is rather silly, but more serious mistakes in
reasoning can also be made through equivocation. For example:
It is lawful to keep an animal is a pen and to feed it once a day.
Ozzy Osborn is a real animal. Therefore, it is lawful to keep Ozzy
in a pen and feed him once a day as well.
OK, this example of equivocation (on the term animal) wasn’t very serious,
but the mistake was serious. How about this one . . .
Since the Constitution declares all men were created equal the government
must give me a million dollar house like my neighbor so we are both equal.
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It should now be apparent that if you want to argue well
you must pay attention to the meaning of words.
In the Appendix (p. 79-85), Weston makes several important
comments about Definitions:
D1: When terms are unclear, get specific
D2: When terms are contested, work from the clear cases
D3: Don’t expect definitions to do the work of the
argument.
It may surprise you how hard it is to define something well.
Try it out . . . define ‘chair’
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If you said ‘something to sit on’ doesn’t that also include the following:
If you narrowed down your definition to ‘a piece of furniture with four legs
How that
cansupports
you improve
definition?
intended for sitting
the back’the
aren’t
you still including the following:
Are these items really chairs?
What do you need to add to the
definition to make it work?
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But does your new definition end up excluding the following
examples?
Should these items be excluded
from any definition of chair? Does
your definition exclude them?
I hope it is clear that it takes time and effort to make a good
definition. Never rush when giving a definition, especially when
your argument depends upon it.
Try some more . . . Define ‘cup’ and ‘fork.’
Make sure to test the definitions to ensure they include all the
correct items and exclude those that do not belong.
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In the second set of slides we will discuss different types of
arguments. In the third set we will discuss common mistakes
in reasoning, called fallacies.
Please contact me with any questions about the information in
these slides or the related assigned reading:
• Weston, Introduction, Chapter 1 and the Appendix
• Logic Handout, pages 1-3 and the chart on page 7