Classical Argumentation and Formal Logic PowerPoint

Classic argumentation and
Formal Logic
Part 1 – Discovery or Invention
Inventio (Discovery or
 Given a topic, the orator had to find arguments to
support his point of view. Inventio is a system for
finding those arguments, and the orator had to
make some carefully prescribed choices:
 Emotional appeal: an analysis and understanding of
the common emotions
 Ethical appeal: gaining the audience’s trust and
admiration through high moral standards.
 Rational appeal: an appeal to reason through
induction or deduction
Pathos or Emotional Appeal
 Writing that appeals only to the emotions of the audience
is generally ineffective.
 However, if one chooses language (figurative language
or personal anecdotes) that engages the emotions of the
audience, pathos can add an important addition.
 Connotation versus denotation
 Using words that have an emotional meaning that is strong
to the reader references connotation. Denotation is the
traditional dictionary definition of the word.
 I would appeal to an audience by saying words like grand,
honored, and blessing in a thank you speech instead of nice
and thank you.
Ethos or Ethical Appeal
(sometimes called Moral appeal)
 Speakers who appeal to ethos demonstrate that they are credible
or trustworthy.
If giving a speech about alcohol and children, for example, a speaker
may be
A concerned parent
A psychologist specializing in alcoholism and adolescence behavior
Or recovering alcoholics themselves.
 It is important to note here that the ethos appeal is not an
argument concerning the ethics of the claim one is making.
For example, I am not arguing that alcoholism is morally or ethically
 Instead it is the speakers expertise and knowledge, experience,
training sincerity, or a combination of these that gives the
audience a reason to listen.
Logos or Logical Appeal
 Logos is an appeal to reason or logic.
 It offers clear, rational ideas.(remember that your
idea must be logical)
 It must have a thesis or main idea,
 Specific details
 Examples, facts, statistical data, and/or expert
testimony (as support)
 Logos is often used to acknowledge a
counterargument (anticipating objections or
opposing viewpoints)
Logos – the Counterargument
 While it may seem raising a counterargument will
weaken your point, you’ll actually seem more vulnerable
if you ignore others’ ideas.
 You acknowledge you concede (agree) that an opposing
argument may be true but…
 You then refute (deny) the validity of all or part of the
 This concession and refutation strengthens your
argument by appealing to logos, which shows you
considered your subject carefully before making your
Types of Logos
 Logos uses two types logical appeal:
 Induction
involves the compiling of evidence /reasons/examples
that support an argument: the amassing of reasons. The
more evidence, the better the argument, but often three
good reasons or examples will do.
 Deduction
 involves premises—statements upon which all parties
agree, which, when considered logically, lead to a
strong conclusion. (Getting all parties to agree on the
premises is often the cause of debate, however.)
 When arguing inductively, you should ask these
1. Are the examples sufficient in number? (Do you
have enough of them?)
2. Are the examples truly representative of the issue?
(Are they relevant?)
3. Do the examples come from a reliable authority or
from logic?
Example of Induction
 Nearly 80% of the ocean pollution comes from runoff.
 Runoff pollution can make ocean water unsafe for fish
and people.
 Drinking water can be contaminated by runoff.
More than one third of shellfish growing in waters in the
United States are contaminated by runoff.
 Each year, millions of dollars are spent to restore
polluted areas.
 There is a casual relationship because of agricultural
runoff and waterborne organisms that damage fish.
 When arguing deductively, you should ask these
1. Are the premises themselves valid or resulting
from strong inductive evidence?
2. Does the conclusion follow logically?
Examples of Deduction
 Major Premise: All good students get financial aid.
 Minor Premise: Sara is a good student.
 Conclusion: Therefore, Sarah should get financial
Examples of Deduction
 Major Premise: When a government oppresses
people, the people have a right to abolish that
 Minor Premise: The government of England is
oppressing the American people.
 Conclusion: Therefore, the American people have
the right to abolish that government.
How it applies?
 We will be discussing this further as the year
progresses. Meanwhile, you should know some
background on argumentation as a formal study
that the ancient Romans called “rhetoric.”
 As we’ve learned, induction involves the compiling
of evidence/reasons/examples that support an
argument: the amassing of reasons.
 If one is arguing inductively, she may say:
 “Wow! My dog smells terrible! She was outside all
night, and around midnight I smelled skunk at the back
of the house. I heard her barking loudly, too. That’s
definitely a skunky smell on her. She must have tangled
with that skunk.”
 This person has amassed sufficient, relevant, and
reliable evidence to draw her conclusion.
 We also recall that deduction involves premises –
statements upon which all parties agree, which
when considered logically, lead to a strong
conclusion. (Getting all parties to agree is often the
cause of debate)
 Syllogism
 The formal statement of a deductive proof.
 It contains a major premise, a minor premise, and a
 Major Premise: A generalization or allencompassing statement.
 Minor Premise: A statement of a specific instance of
the generalization.
 Conclusion A statement of conclusion which
follows the premises.
 The classic example is
 All human beings are mortal.
 Socrates is a human being.
 ∴Socrates is mortal.
 ∴ means therefore.
 Syllogisms are seldom found in their pure
form but instead appear in the form of
 An enthymeme is a syllogism with one or
two parts of its argument – usually the
major premise – missing.
 In everyday life, we often leave out part of
the arguments – most of the time because
we think they are so obvious (or clearly
implied) that they don’t need to be stated.
 Many enthymemes are presented as a
conclusion plus a reason.
 The enthymeme can be understood as an
abbreviated syllogism because
 It resembles the syllogism in that it
employs logic.
 It has as its starting pont an assumption,
statement, or proposition that the
writer/speaker presumes the audience
 We recognize that part of the argument
goes unstated.
 One way of explaining the strategy of the
enthymeme is this:
 “Statements may be strategically excluded in an
enthymeme because they are too obvious or
because revealing them might damage the force of
the argument. Yet another reason to exclude a
premise or conclusion is to let the audience infer it.
The idea here is hat audiences who have to draw
out premises or conclusions for themselves are
more likely to be persuaded by the overall
argument.:” –
 Enthymeme : Robert has lied, so he cannot
be trusted.
 In the statement above, the minor premise and
conclusion are stated, but the major premise is
only implied.
 Major Premise: People who lie cannot be trusted.
 Minor Premise: Robert has lied.
 Conclusion: Therefore, Robert cannot be trusted.
 Enthymeme : Robert cannot be trusted.
 In the statement above, the major premise and
minor premise are implied, and only the
conclusion is stated..
 Major Premise: People who lie cannot be trusted.
 Minor Premise: Robert has lied.
 Conclusion: Therefore, Robert cannot be trusted.
 It is important to identify enthymemes in arguments
you read because some writers, knowing that readers
often accept enthymemes uncritically, use them
intentionally to unfairly influence readers.
 Enthymeme: Because Liz receives a tuition grant, she
should work.
 Major Premise: All students who receive a tuition grant
should work.
 Minor Premise: Liz received a tuition grant.
 Conclusion: Therefore, Liz should work.
 How is this enthymeme oversimplifying the issue?
 Bumper Sticker Thinking
Self-Control beats birth control.
Peace is patriotic.
A woman’s place is in the White House.
Ban cruel traps.
It’s never too late to have a happy childhood.
No one needs a mink coat except a mink.
Celebrate diversity.
Enthymeme vs. Syllogism
 A fully stated syllogism where both
premises are accepted as universally true,
leads us to necessary conclusion based on
its proven validity.
 But
 An enthymeme, where the implied premise
can be stated either of two was, leads us to a
tentative conclusion based only on probable
premises, which therefore may be arguable.