2. Logic for Legal Reasoning
• Logic and the law are intertwined
• Law schools don’t always teach logical
reasoning or argument
• Most righting and speaking in the legal
profession is based upon logical arguments
• You cannot read case like a lawyer until you
understand the basics of logical thinking
3. Logical Reasoning for
Lawyers
• A basic command of logical reasoning is
needed to follow most legal arguments
• Critical to success in the law school
classroom
• Central to effective engagement in Socratic
dialog
• Not required to know the ins and outs of all
logical reasoning just the basics
4. Three Forms of Logical Reasoning Every
Reader of the Law Should Know
• Deductive reasoning
– Proving a conclusion by means of two other propositions
– By far the most frequently used form of reasoning
conclusions under the law
• Inductive generalization
– Arriving at sweeping generalizations based upon a smaller,
more discrete event
• Analogy
– The comparison of two different things in order to draw a
conclusions about both (EXTREMELY IMPORTANT IN LAW
SCHOOL!)
5. Deductive Reasoning
• One of two main forms of logical reasoning
• Important to the legal system and reasoning
since this form of reasoning provides a
grounded foundation for conclusions
• Deduction in reasoning in which a conclusion
is compelled by facts
• If A and B are true so must C
• John is 6 feet tall; Susan is taller than John;
Susan must be taller than 6 feet
6. Deduction and Legal
Reasoning
• Syllogistic reasoning is the deductive
reasoning that is also used in judicial
opinions, briefs and memos
• Instead of a result being COMPELLED by two
FACTS it is instead INFERRED from two
PREMISES
• Major premise + minor premise = conclusion
• What is true of the universe is true of the
particular
7. Example
• All people sleep (general) so students must
sleep (particular)
• Major premise (general): All people sleep
• Minor premise (particular): Students are
people
• Conclusion: Students sleep
8. Syllogism lies at the heart of
legal writing
• Griswold v. Connecticut
• A law is unconstitutional if it impacts the
zone of privacy created by Bill of Rights.
• The law banning contraceptives impacts
the zone of privacy created by the Bill of
Rights.
• Therefore the law banning
contraceptives is unconstitutional
9. Learn to Think in Syllogisms
• Daily study is required to be a good student
• I study daily
• I am a good student
• If you are not making syllogistic arguments in
your case briefs, legal writing, exams etc you
will never succeed in law school.
10. How do you develop the skill of
thinking/reasoning in syllogisms?
• Construct a general rule as a major premise
– Widely known legal rule
– Applicable and relevant to your facts
• Construct a minor premise for your facts
• Draw a conclusion based upon how that
general rule applies to the minor premise
about facts
11. Example
• Major premise: The First Amendment protects
certain kinds of expression from being
banned
• Nude dancing is a form of expression
protected by the first amendment
• The government cannot ban people from
dancing without clothing
12. Think of a Generic Syllogism
for Each Area of Law
• Constitutional (rights of individuals)
– [Doing something] is protected by [constituional
basis]
– [Plaintiff] was [Doing something]
– [Plaintiff] is protected by [constitutional basis]
• Can you think of one for criminal law?
Contracts? Torts?
13. Not always easy to find in
judicial opinions
• Excess language may obscure the logical
reasoning
• Doesn’t mean it’s bad writing
• The law, after all, is complex!
• Once you find it, however, you can argue its
validity or applicability--so you have to find it!
14. Example
• This right of privacy, whether it be founded in
the Fourteenth Amendment’s concept of
personal liberty and restrictions upon state
action, as we feel it is, or, as the District Court
determined, in the Ninth Amendment
reservation of rights to the people, is broad
enough to encompass a woman decision
whether or not to terminate her pregnancy.
16. • Major Premise: The right of privacy is
guaranteed by the Fourteenth or Ninth
Amendment.
• Minor Premise: A woman’s decision to
terminate her pregnancy is protected by the
right of privacy.
• Conclusion:Therefore, a woman’s decision
whether to terminate her pregnancy is
protected by the Fourteenth or Ninth
Amendment.
17. Sometimes judges leave
things out that you should
know…
• No matter how much rearranging of language
you do you may be stuck!
• Efficiency means stuff gets left out especially
when so widely known that both parties would
accept that fact
• Be on the lookout for this kind of scenario
18. Pollysyllogisms
• Multiple syllogisms must be constructed in
order to establish a conclusion
• Most judicial opinions are written this way
• Rule based syllogisms get stacked upon one
another in order to create holdings
• Hosanna-Tabor case
19. Warning!
• Watch out for flawed syllogisms
• Sometimes the major premise is not ‘major’
enough
• If not encompassing it leaves room for an
opening in order to undercut the argument
• Look for qualifying language like some,
sometimes, many, once, occasionally,
oftentimes etc.
20. Example
• Major Premise: Some forms of
expression are protected by the first
amendment
• Minor Premise: Nude dancing is a form
of expression
• Conclusion: Nude dancing is protected
by the first amendment
21. Inductive Reasoning
• Big, general principles are divined from
individual smaller events
• Opposite of deductive
• Instead of general to specific induction is
taking specific to general
• The world is predictable enough to arrive at
conclusions based upon specific incidents
that frequently occur
• Not guaranteed…
22. Example
• Jane studies every day and is a good
student.
• Tom studies every day and is a good
student.
• Angela studies every day and is a good
student.
• Good students study every day.
23. When is inductive reasoning
used?
• When there is insufficient precedent
• No clear statute
• Basically, no major premise!
• Easiest to understand but hardest to use
• Law students oftentimes default to it when in
classroom dialog
• One example of the opposite of the particular
statements (e.g. Randy is a good student but
he never studies) is all that is needed to
undermine them
24. Analogy
• Plays a critical role in oral argument
before appellate panels and most law
school classrooms
• Used to test the validity of an argument
• Mastering the use of analogy is one of
the most crucial aspects of
thinking/reading like a lawyer (as well as
law school and legal practice)
25. Structure of Analogy
• A has characteristic C
• B has characteristic C
• A also has characteristic D
• Because A and B share C they must
share D as well
26. Useful to legal reasoning
• Current cases get compared to new
ones
• Established precedent gets applied to
new factual scenarios
• Critical to judicial opinions
27. How does it work?
• Establish similarity between two cases
• Announce the rule of law embedded in the
first case
• Apply the rule of law to the second case
• Process of reasoning from particular to
particular
• The reasoning process becomes more about
establishing or debunking the similarities
between the two cases
28. Example
• You are issued a citation for driving a scooter
without a helmet
• Case 1 prohibits riding a motorcycle without a
helmet
• Case 2 allows riding a bike without a helmet
• Is a scooter a really fast bike or a slow
motorcycle?
