Logos: Using Logic and Evidence Effectively

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Logos Using Logic and Evidence Effectively
By Kristi Wilson, Graduate Associate
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RHETORICAL PROOFS

• All arguments require a claim and justification,
  or support.

• Rhetorical proofs are types of support.

• Three types of rhetorical proofs

• Ethos ethical appeal (authors credibility)
• Pathos emotional appeal (audiences emotion)
• Logos logical appeal (audiences reason)

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WHAT IS LOGOS?

• What are the various types of logical proofs we
  can use in an argument?

Statistics/data (incl. surveys, interviews, etc.)
Definitions
Deductive reasoning (x, y, and z, are
true therefore I conclude ____.)
Inductive reasoning (I claim ____ because x, y,
and z.)
Analogies (historical, literal)
Hypothetical examples predicted outcomes
ALWAYS EXPLAIN THE CONTEXT OF YOUR EVIDENCE
AND/OR PROVIDE ANALYSIS/INTERPRETATION!
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WHEN FACTS ARE AT ISSUE

• How can facts be at issue? Arent facts beyond
  question?

• Facts might be interpreted differently based on
  values, beliefs, biases, preconceptions, goals,
  etc. Therefore, using facts is an ethical act.

• Ask questions about your issue this will
  require putting aside what you think everyone
  knows and thinking critically about the issue

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GET YOUR FACTS STRAIGHT

• Be sure to clarify terminology to avoid conflicts
  over facts (e.g., welfare example in Weston, p.
  138)

• When the facts are uncertain, looking deeper
  is necessary (Weston 138). Why?

• Evidence is always required dont tell me its
  a known fact. Show me the evidence!

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A WORD ON SOURCES

• In order to use facts in an authoritative and
  convincing way, we must be explicit and specific.

• Cite trustworthy sources

• Use plentiful and specific statistics and/or
  examples

• Explain the context and interpret the data

• Use sound reasoning

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LOGICAL STRUCTURE

• Claims are supported/justified by reasons
  (because/therefore)

• Effective logical appeals (logos) require more
  than just the facts you must be sure you
  present your evidence using a clear, logical
  progression and sound reasoning

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ASSUMING THE OBVIOUS?

• All claim/reason pairs have unstated assumptions
  (a.k.a. warrants) which allow the reader and
  writer to make the logical leap between the
  reason and the claim

• If the audience doesnt share the assumptions,
  the argument will be ineffective. Be sure your
  audience shares your assumptions.

(Turn to examples in exercise on p. 90)
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AUDIENCE-BASED REASONS

• Arguments are more effective when they take the
  audiences goals, values, and motivations into
  consideration.

(See examples in exercise on p. 104)

• For a list of questions to help you determine how
  best to approach your audience, see p. 105.

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CORRELATION TO CAUSE

• According to Weston, to make an effective causal
  argument, we must

• cite accurate correlations
• explain how the (proposed) cause leads to the
  (proposed) effect and
• argue that the proposed cause-effect relationship
  is the best explanation of the correlation.

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CORRELATION TO CAUSE

• Correlations can be explained in a variety of
  ways. Test these various scenarios against your
  issue to determine its relationship to
  globalization

• X is an effect of globalization
• Globalization is an effect of X
• X is an effect of globalization and globalization
  is an effect of X
• Globalization and X are both an effect (or cause)
  of Y or
• Globalization and X are coincidental and have no
  causal relationship.

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CORRELATION TO CAUSE

• A good argument about causes or effects must
  both explain how the proposed cause could lead to
  the proposed effect...and it must try to show
  that the proposed explanation is the best or most
  likely explanation of the observed correlation
  (Weston 143-44).

Sources Ramage, John D., John C. Bean, and June
Johnson. Writing Arguments A Rhetoric with
Readings. New York Pearson, 2004. Weston,
Anthony. A 21st Century Ethical Toolbox. New
York Oxford UP, 2001.