Logic for Legal Reasoning

LIBR 430 Week 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

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

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!)

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

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

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

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

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.

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

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

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?

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!

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.

The syllogism?

• Major Premise?• Minor Premise?• Conclusion?

• 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.

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

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

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.

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

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…

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.

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

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)

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

Useful to legal reasoning

• Current cases get compared to new ones

• Established precedent gets applied to new factual scenarios

• Critical to judicial opinions

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

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?