8 Ways to Compare Evidence
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I did not frequently use the tactics I am about to explain to you. However, when I did use
them they were crucial in determining the outcome of the round, and it is therefore
essential that you understand these methods of evidence comparison, as well as, perhaps
more importantly, when and when not to use them.
Why should you compare evidence?
o Can be the deciding factor in determining whether you are winning a particular
argument. Every argument needs a claim, warrant and impact, and if your
opponent successfully indicts a piece of evidence that constitutes your warrant for
an argument, you are no longer in control of that argument
o Perceptual dominance: speaking persuasively about author qualifications, source
quality, postdating, p-values, etc. indicates to the judge that you totally understand
your arguments and how they interact with your opponent’s
When should you compare evidence?
o When you and your opponent use two different pieces of evidence that make
opposite claims
o When one piece of evidence precludes, undermines or mitigates the argument
made by another piece of evidence
SO LET’S GET TO IT
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Evidence is defined as any support provided for the truth of an assertion. Some people
believe that carded evidence is necessary to win an argument, some people do not. You
should be somewhere in the middle. Do not be dismissive of non-carded assertions, but
do not miss the value of cards. Authors, in general, make better arguments than does a
debater or debate coach.
Basis for comparison
o Comparing warrant strength:
 1. In your card, identify the warrant
 2. When you compare against an opponent’s card, identify his or
her warrant. Isolate the justifications for the claims.
 1. Evidence that is DEEP-WARRANTED provides more support than
evidence that has a SHALLOW warrant.
 2. Qualifiers
 E.g. This “may” happen. A type of condition. An adverb that
lessens the strength or scope of a warrant. NO ONE wants to
underline those qualifiers, so probe their evidence carefully.
 Qualifiers speak to probability. Use the qualifying language to set
up a comparison on the basis of probability.
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THE ESSENCE OF DEBATE IS WARRANT COMPARISON
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3. The date
 Often referred to as “postdating”
 Identify the date for your card; identify your opponent’s date. IF
they do NOT have their dates, they lose the perceptual battle.
 Post-dating is relevant IF circumstances have changed (e.g. his
evidence is from 1988, mine is from 1992. Mine is preferable,
because the Cold War ended in 1991, so the claims his authors
make about international relations and conflicts are based on
geopolitical situations that are no longer relevant).
4. Author’s predictions (this is underutilized; I myself never used this
tactic, and you should use it only when you are familiar with BOTH of the
authors that wrote the conflicting pieces of evidence)
 Many international relations authors write passages (that have been
turned into cards) that have implicit predictions about the world,
and those predictions turned out to be false. Isolating a false
prediction in the opponent’s evidence decreases (but does not
necessarily undermine) the credibility of that source; exposes the
falsity of some of their assumptions.
5. Author’s qualifications (there is a hierarchy in the academic world;
however, as we will see, higher does not necessarily translate into better
quality evidence)
 Professor Emeritus (professor has so much experience at the
professor level that his university gives him a special office, where
he stays on even after he retires)
 Full Professor (tenure track)
 Associate Professor (on tenure track)
 Assistant Professor (young in terms of experience)
 Adjunct Professor (doesn’t teach full time)
 Professor at Practice (a lawyer vs. a law professor. Usually do not
have the same advanced degree as a full professor, for example)
 HOW TO COMPARE AUTHOR QUALIFICATIONS:
o A Professor Emeritus is more experienced, considers more
variables, anything he or she writes is held to a higher
standard, more likely to be peer reviewed. The value of
their experience is greater, because they’ve been working
in a particular subject matter for a much longer period of
time than most other professors
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o Beware of the fallacy of appealing to authority. You can
get out of this fallacy by establishing that the claim in
question is probabilistic, so more knowledge on the subject
(i.e. that of a PE vs. AP) increases the strength of the
probabilistic claim
o PE is not always the best source of evidence (PE has more
room to move around in/most have retired, and therefore
are not as engaged in their fields. Associate Professor is
much more involved in the actual research and practice, so
what they say is more relevant and accurate)
 Determine what the author’s qualifications were WHEN HE OR
SHE WROTE THE PAPER, NOT WHAT THEY ARE NOW
6. Author’s field
 The more relevant a field is, the more likely a person in that field is
going to get it right
 E.g. “Resolved: In the United States, juveniles charged with
violent felonies ought to be treated as adults in the criminal justice
system.” Steven Levitt has a degree in economics, not criminology
or sociology, so his opinion on this resolution is not relevant.
o Response: Economists have statistical expertise. Fields can
(and, in this case, do) overlap in significant ways. Further,
the economist has no incentive to reach a certain
conclusion, whereas a Professor of Criminal Justice may
work in rehabilitative organizations, and so might have a
bias that affects his writings.
o BEWARE of the MOTIF FALLACY: the fact that you are
self-interested to say something does not necessarily mean
that the content itself is wrong
7. Article awards!
 If an article receives a nice award, it appears more
credible/authoritative
Notes in LexisNexis
o Law students write these!! “Note:” was written by someone who has not yet
graduated law school, so they have, at most, completed 2-3 years of law school,
and don’t have as large a basis for analysis
o NO LAW REVIEW ARTICLE IS PEER-REVIEWED
 Use Anjan’s anecdote (his predictions were terribly inaccurate!)
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o HOWEVER, law students want to do exceptional work; they are on the cutting
edge, ambitious. Graduate students tend to do most of the actual research for
studies published by professors. Further, students don’t have as entrenched a
conviction/their views are developing.
o ONLY make these arguments when the authority matters; otherwise, it’s simply
an appeal to authority
o The more technical the argument, the more crucial this type of comparison is
o The more empirical, the more crucial
BEWARE of AD HOMINEN ATTACKS
o E.g. Martin Heidegger’s opinions mean nothing because he was a member of the
Nazi party
o Ad hominen attack—debasing the argument based upon the merit of the speaker
o You need to explain why what you’ve established is relevant to the merits of the
argument; do NOT just challenge his character!!
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8. Source Quality: what type of article/book/source is it? Compare!!
 4 basic categories:
o Peer-review studies (e.g. International Security Journal)
o Qualified authors whose studies are not peer reviewed (e.g.
think tanks)
o “Lay” publications (newspapers, magazines)
o GARBAGE
 Blogs, UNLESS written by professors (many wellestablished professors have regular blogs)
 Why might a peer-reviewed study not be as good? It takes a LONG
time for such a study to be published, so the information included
in the study, though it was probably correct when the author wrote
it, may not be true 2-3 years later, when the study is published in a
journal. Thus, when your opponent argues that his peer-reviewed
study was published in 2010, the reality is that it was actually
written in about 2008.
You can compare methods of evidence comparison: e.g. you can argue that postdating
overwhelms the fact that your warrant is not as strong
EVIDENCE COMPARISON TACTICS
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Call for the case before CX starts
o Read cards aloud when asking questions!!
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Ask specifically about 1-2 lines in his card
Hone in on the un-underlined parts of the evidence
Dominant perceptually and substantively
YOU CAN AND SHOULD KILL HIS CREDIBILITY
If you can’t read the small print, EMPHASIZE IT in CX
Ask about the source and qualifications of the author. If they don’t have them,
you kill his credibility
o Check the title of the article from which your opponent cut evidence for his case
 This could clue you in to a potential straw man argument (not respecting
the author’s intent; debaters often cut cards from an article whose
conclusion is the opposite of the claim made in that particular card)
o Confusing a necessary and a sufficient condition
o Scrutinize their tag-lines
o Beware of the fact that debaters over claim their impacts all the time!!!
Prep-time
o See if each new card discusses the same issue as the previous card. You can, in
rebuttals, argue that your opponent is equivocating (taking arguments out of
context)
o See whether the author poses a question or draws a conclusion (“this is a research
agenda” is much less powerful than “this is my answer”)
Rebuttals
o In rebuttals, ALWAYS be COMPARATIVE between evidence (“my evidence is
better than his, because…”)
o Figure out what their best cards are, then argue why your evidence is better, even
if you know you’re wrong (if might scare them off of their best card!)
o Challenge the guts of the card; don’t lose because you weren’t responsive to the
specific internal warrants in a card