Lecture 9:
Analyzing Arguments –
Diagramming Short Arguments
This is a bit of historical documentation of what
Spring Breaks were like when I was an
undergraduate (well, really when I was still in
high school) ….
Welcome Back from Spring Break
Today: Analyzing Arguments
But first, a fallacy in the news …
Can you spot it? What kind of fallacy is this?
• What Obama said re. Trayvon Martin
• What Gingrich said Obama said re. Trayvon
Martin
Arguments – Review
• Arguments consist of premises and
conclusions.
• Premises and conclusions are statements.
Arguments – Review
• Premise indicator words: since, because, for,
given that, seeing that, considering that, inasmuch
as, as, in view of the fact that, as indicated by,
judging from, on account of
• Conclusion indicator words: therefore, thus,
hence, consequently, so, accordingly, it follows that,
for this reason, that is why, which shows that,
wherefore, this implies that, as a result, this suggests
that, this being so, we may infer that.
Diagramming Short Arguments
• Argument:
The death penalty should be abolished because
it’s racially discriminatory, there’s no evidence
that it’s a more effective deterrent than life
imprisonment, and innocent people may be
executed by mistake.
Diagramming Short Arguments
• Step 1: Identify (circle, underline, etc.) all
premise and / or conclusion indicators.
The death penalty should be abolished because
it’s racially discriminatory, there’s no evidence
that it’s a more effective deterrent than life
imprisonment, and innocent people may be
executed by mistake.
Diagramming Short Arguments
•
Step 2: Number the statements consecutively as
they appear in the argument.
1) The death penalty should be abolished
2) because it’s racially discriminatory,
3) there’s no evidence that it’s a more effective
deterrent than life imprisonment, and
4) innocent people may be executed by mistake.
Diagramming Short Arguments
• Step 3: Arrange the numbers on a page with
the premises placed above the conclusion(s)
they claim to support.
2)
3)
1)
4)
Diagramming Short Arguments
• Step 4: Omit any logically irrelevant statements.
• Step 5: Use arrows to mean ‘is offered as evidence for’
to show relationship of argument support.
2)
3)
4)
1)
Here 2), 3), and 4) offer independent support for the
conclusion.
Diagramming Short Arguments
•
A premise provides independent support for a
conclusion when the amount of support it provides
would not be weakened or destroyed by the removal of
any other premise in the argument.
• A premise provides linked support when it works
conjointly with another premise to support the
conclusion:
EXAMPLE: No member of the SJSU community is a fan of the
Leland Stanford Junior University Marching Band.
Maurice is a member of the SJSU community. So,
Maurice is not a fan of the Leland Stanford Junior
University Marching Band.
Diagramming Short Arguments –
Linked Support
1) No members of the SJSU community is a fan
of the Leland Stanford Junior University
Marching Band.
2) Maurice is a member of SJSU community.
3) So, Maurice is not a fan of the Leland
Stanford Junior University Marching Band.
Diagramming Short Arguments
Linked Support:
1)
+
3)
2)
Linked or Independent Support?
• Linked: Omission of one
• Independent: Neither
premise cancels / reduces
premise would provide
support provided by the
less support for the
other.
conclusion if the other
were omitted.
Example:
• Example:
No student in Ling 21 is a
Rhodes Scholar.
Nick doesn’t own a car.
Nick is legally blind.
Josue is a Rhodes Scholar.
So Nick probably won’t
So, Josue is not a student in
drive a car to the game.
Ling 21.
Linked or Independent Support?
• Ten witnesses say they saw Blotto rob the
bank. The stolen bank money was found in
Blotto’s car. Blotto’s fingerprints were found at
the Teller’s window. Therefore, Blotto
probably robbed the bank.
• If Amy runs marathons, then she’s probably
very fit. Amy does run marathons. So Amy
probably is very fit.
Other Kinds of Support
1) Jim is a senior citizen.
2) So, Jim probably doesn’t like hip-hop music.
3) So, Jim probably won’t be going to the Ashanti
concert tonight.
1)
2)
3)
Other Kinds of Support
Example:
Most Democrats are liberals, and Senator
Dumdiddle is a Democrat. Thus, Senator
Dumdidle is probably a liberal. Therefore,
Senator Dumdiddle probably supports
affirmative action in higher education, because
most liberals support affirmative action in higher
education.
Other Kinds of Support
Example:
1)
2)
3)
4)
Most Democrats are liberals, and
Senator Dumdiddle is a Democrat.
Thus, Senator Dumdidle is probably a liberal.
Therefore, Senator Dumdiddle probably supports
affirmative action in higher education,
5) because most liberals support affirmative action in
higher education.
Other Kinds of Support
• Premises and conclusions:
1)
+
3)
2)
+
4)
5)
Other Kinds of Support
Cheating is wrong for several reasons. First, it will lower
your self-respect, because you can never be proud of
anything you got by cheating. Second, cheating is a lie
because it deceives other people into thinking you know
more than you do. Third, cheating violates the teacher’s
trust that you will do your own work. Fourth, cheating is
unfair to all the people who aren’t cheating. Finally, if
you cheat in school now, you’ll find it easier to cheat in
other situations later in life – perhaps even in your
closest personal relationships.
Other Kinds of Support
1) Cheating is wrong for several reasons.
2) First, it will lower your self-respect,
3) because you can never be proud of anything you got by
cheating.
4) Second, cheating is a lie
5) because it deceives other people into thinking you know
more than you do.
6) Third, cheating violates the teacher’s trust that you will
do your own work.
7) Fourth, cheating is unfair to all the people who aren’t
cheating.
8) Finally, if you cheat in school now, you’ll find it easier to
cheat in other situations later in life – perhaps even in
your closest personal relationships.
Other Kinds of Support
Notice the use of because in 3) and 5):
3)
5)
2)
4)
Other Kinds of Support
• Note that 2), 4), 6), 7), and 8) all provide
independent support for the main conclusion 1):
3)
5)
2)
4)
6)
1)
7)
8)
Tips on Diagramming Short Arguments
• Find the main conclusion first
• Pay close attention to premise and conclusion indicators.
• Remember: sentences containing the word ‘and’ often
contain two or more separate statements.
• Treat conditional statements (if-then) and disjunctive
statements (either-or) as single statements.
• Don’t number / diagram any sentence that is not a
statement.
• Don’t diagram irrelevant statements.
• Don’t diagram redundant statements.
Practice
Critical Thinking, p. 171-75, Exercise 7.1
• Step 1: Identify (circle, underline, etc.) all premise and /
or conclusion indicators.
• Step 2: Number the statements consecutively as they
appear in the argument.
• Step 3: Arrange the numbers on a page with the
premises placed above the conclusion(s) they claim to
support.
• Step 4: Omit any logically irrelevant statements.
• Step 5: Use arrows to mean ‘is offered as evidence for’
to show relationship of argument support.