Evidence in Argumentation Study Notes

Role and Structure of Evidence in Argumentation

Evidence is the primary building block advocates use to support assertions and increase their acceptability when listeners ask questions like "What do you have to go on?" or "What makes you say so?". For argumentation to succeed, all participants in a dispute must agree on the basic truth of the evidence presented, even if they disagree on its interpretation, meaning, or relevance to the claim. When a party does not accept the factual truth of a statement of evidence, the advocate must provide additional backing or support for that evidence.

Evidence must satisfy critical standards of quality. Widespread audience agreement alone does not make evidence acceptable if it lacks critical validity; for example, uncritical acceptance of astrology, conspiracy theories, or social media "fake news" fails to satisfy critical judgment because such assertions do not square with verifiable reality. An arguer exercising critical judgment must evaluate whether a piece of evidence renders the claim more likely to be true than it would be in the absence of that evidence.

Categories of Evidence

Objective Data

Objective data consists of independently verifiable statements that do not rely on an arguer's personal intervention or subjective bias. Anyone utilizing established procedures or measurements can investigate objective data and reach identical results, although the interpretations and political or social meanings derived from those data may still be disputed (such as interpreting an unemployment rate of $5.0\%$ based on economic trends):

• Examples: Specific instances that make abstract ideas concrete:

  • Brief Allusions: Quick mentions intended to assure the audience that supporting instances exist and could be expanded upon.

  • Illustrations: Detailed, fully developed stories or case studies (e.g., recounting a specific family's loss during a natural disaster to demonstrate general suffering).

  • Note: Examples function both as evidence and as reasoning schemes.

• Statistics: Quantitative measurements of enumeration or comparison:

  • Raw Numbers: Simple enumerations (e.g., $4,500$ U.S. soldier casualties in Iraq by $2010$, or exactly $2$ father-son U.S. presidential pairs by $2020$).

  • Percentages, Ratios, and Index Numbers: Comparative quantitative metrics, such as percentages ($55\%$ of baby boomers planning to work past age $70$), ratios ($8$ to $1$ ratio of women to men in nursing school showing relative group strength), and index numbers (setting a base year like $1995$ to $100$ to show gas prices rising to $280$).

  • Measures of Central Tendency: Metrics determining "average" clustering around a central data point:

  • Mean: The arithmetic average obtained by dividing the sum of values by the total count; can be skewed by extreme outliers.

  • Median: The exact middle score when values are ordered from highest to lowest; can be misleading if data points are widely scattered without a clear central cluster.

  • Mode: The most frequently occurring score; can be misleading if the sample size selecting any single option is small.

  • Rates of Change: Metrics demonstrating the velocity of transformation (e.g., Las Vegas adding $20,000$ residents per day prior to the $2008$ real estate collapse).

  • Probability Statements: Expressions of statistical confidence (e.g., results significant at the $0.05$ level of confidence, meaning that out of $100$ repetitions, $95$ occurrences reflect experimental design while $5$ occur by random chance).

• Tangible Objects and Documents: Physical artifacts and official texts brought forward to ground arguments directly in "the thing itself" (e.g., a murder weapon, the O.J. Simpson glove, pumpkin microfilm in the Alger Hiss case, the Zapruder film, Colin Powell's UN presentation materials, or constitutional texts like the Bill of Rights, UN Declaration of Human Rights, legal precedents, and labor contracts).

• Direct Observation: Empirical firsthand reports ("seeing is believing"). While valuable, observations are vulnerable to perceptual distortion (e.g., lighting, distance, color-blindness) and confirmation bias (seeing what one expects or wishes to see), making eyewitness testimony subject to critical scrutiny.

Social Consensus

Social consensus depends on widespread assent among critical listeners rather than independent empirical verification:

• Commonplaces: Deeply entrenched social beliefs accepted as self-evident truths without requiring further proof, establishing strong presumptions (e.g., "Politicians manipulate budget numbers" or "You can't trust Washington"). Challenging a commonplace places a heavy burden of proof on the advocate.

• Shared Value Judgments: Broadly held preferences and moral commitments (e.g., wanting what is best for one's children, seeking to avoid war whenever possible, and showing respect for older generations).

• Shared Historical Understandings: Commonly accepted "lessons of history" and historical interpretations (e.g., the U.S. winning the Cold War, or the Civil Rights movement securing major gains through protests in the $1950\text{s}$ and $1960\text{s}$).

• Previously Established Claims: Arguments that have already been established with sufficient proof and can now serve as foundational evidence for subsequent claims.

• Stipulations: Formal agreements by disputing parties to accept specific facts as true or waive them from active dispute to streamline argumentation (e.g., attorneys stipulating a witness's credentials or a defendant's location).

Testimony

Testimony consists of factual or evaluative statements provided by a qualified source:

• Credibility: Grounded in true domain expertise and historical track record rather than fame or celebrity status (e.g., athletes endorsing medicines trade on fame rather than relevant expertise).

• Track Record: The demonstrated history of reliable judgment over time (e.g., a stock market analyst or pollster whose past predictions have proven accurate).

• Position to Know: A source's direct access to relevant facts (e.g., an eyewitness at an accident scene or a homemaker observing inflation's impact on household grocery spending may be in a better position to know than an external analyst).

• Self-Interest (Eager vs. Reluctant Testimony):

  • Eager Testimony: Statements that advance the source's own self-interest, carrying lower credibility due to potential bias.

  • Reluctant Testimony: Statements made against one's own self-interest (e.g., a wealthy individual advocating for higher taxes on the rich), which carries high credibility because it is unlikely to be motivated by personal gain.

Locating Evidence

• Search Engines: Algorithms in tools like Google, Bing, and Yahoo! retrieve and rank web results by perceived relevance or hit frequency, though high traffic does not guarantee credibility. Specialized search tools include Google Scholar (academic journals), Google Books, and Google Images. Precise syntax (such as quotation marks around exact phrases) improves search accuracy.

• Electronic Databases: Specialized subscription networks like EBSCOhost, JSTOR, ProQuest, Project MUSE, and LexisNexis provide peer-reviewed, academic, and full-text records that are unavailable on open search engines.

• Catalogs & Libraries: Online library catalogs and global registries like WorldCat (www.WorldCat.org) link users to holdings across more than $10,000$ libraries worldwide.

  • Benefits of Physical Libraries: Access to non-digitized rare sources, serendipitous browsing of adjacent shelf items, access to proprietary subscription databases, and expert guidance from professional librarians.

• Matching Research Scope to Stakes: The depth of required evidence depends on argument stakes: informal debates require simple review sources (e.g., Yelp), university budget disputes require financial data, and public health policy decisions require extensive multi-faceted research. Advocates should always maintain a surplus of evidence to select the strongest grounds and avoid overstating claims.

Evaluating Evidence

The Problem of Evidence Acceptance

People frequently accept weak or fabricated evidence ("fake news") when it matches their pre-existing beliefs, sounds reassuring, or is delivered in an authoritative tone. Tone and delivery often improperly outweigh content in audience evaluations.

Case Study: Flaws in Evidence Evaluation

Colin Powell's $2003$ UN Security Council presentation advocating military action in Iraq illustrates how structured arguments can fail when underlying evidence is flawed:

• Translation Bias: Intercepted phone calls were translated with interpretations skewed toward preferred policy outcomes.

• Forced Patterns: Historical facts were fit into an artificial pattern driven by the desire to demonstrate a clear threat.

• Unverified Sources: Intercepted testimony came from sources of unknown credibility.

• Misinterpreted Visuals: Photographic evidence was treated as self-evident when visual images require context and interpretation across cultural boundaries.

• Logical Fallacies: Arguments relied on "absence of evidence is not evidence of absence" (assuming undisclosed destruction proved weapons were still present).

General Evaluation Standards

James A. Herrick outlines core criteria for evaluating evidence of any type:

1. Accessibility: Evidence must be open and available for public inspection, verification, and replication.

2. Credibility: Sources, data collection methods, and sampling must be reliable and free from bias.

3. Internal Consistency: Statements must not contradict themselves or undermine their own claim (e.g., Abraham Lincoln ending a calm speech on reason with passionate, emotional outbursts).

4. External Consistency: Evidence must align with established facts from independent sources (e.g., claims of mass voter fraud vs. statistical data showing insignificance).

5. Recency: Data must be timely when time sensitivity impacts accuracy (e.g., $2012$ unemployment statistics becoming invalid after subsequent drops).

6. Relevance: Evidence must directly bear on the specific claim being argued.

7. Adequacy: The scope and quantity of evidence must fully support the scope of the claim.

8. Accuracy: Characterizations of evidence must match its true wording, definitions, and timeframes.

9. Context: Original meaning must be preserved without selective editing or misleading quotes (e.g., truncating film reviews).

10. Appropriateness to Purpose: The category of evidence must fit the claim type (empirical measurements for quantifiable facts; credentialed testimony for evaluative judgments).

Evaluating Internet Evidence

Web publishing lacks traditional editorial gatekeeping, peer review, and resource constraints:

• Website Appearance: Professional design does not guarantee accuracy and can be used deceptively (e.g., phishing sites).

• Core Evaluation Precautions:

  • Basic Standards: Verify clear sponsorship, contributor credentials, and factual confirmability.

  • Creator & Domain: Identify who operates the site. Standard domains like .edu (educational) and .gov (government) generally offer greater reliability than .org or .com.

  • Credentials: Check author expertise and account for ideological agendas.

  • Purpose: Determine whether the site aims to inform, advocate, or sell products/services.

  • Scholarship: Look for scholarly indicators such as citations, acknowledgment of limits, fair representation of alternative views, and critical analysis.

  • Confirmability: Cross-check web findings against established print or reputable online sources, avoiding circular self-sealing reasoning or definitions true by tautology.

  • Recency: Confirm when the site was last updated to prevent using obsolete data.