Hello George 47,
I enjoyed researching this question.
I have included references to cases within parts one and two of your
question, I hope you don?t mind.
For an excellent explanation of deductive reasoning in general.
Deductive reasoning is frequently used in the legal profession and in
Judges use it when they wish to come to a legal conclusion based on
tradition or historical practice:
The states may place limitations upon the right to marry
Historically, marriage has been defined as between a man and a woman
Therefore prohibiting same-sex couples from marrying is not unconstitutional
See Baker v. Nelson 191 N.W.2d 185
They also use it to interpret legal authority, such as in the
decisions of Supreme Court Justice Antonin Scalia. See for example
his dissent in Planned Parenthood of Eastern Pennsylvania v. Casey, in
which he opines that the right to choose abortion is not a liberty
protected by the Constitution because ?(1) the Constitution says
absolutely nothing about it, and (2) the longstanding traditions of
American society have permitted it to be legally proscribed.? (505
In other words, because a legal authority does not directly and
literally allow something and it has historically been considered
illegal, a law that proscribes the thing must be a valid law.
In a sense, one could say that the law?s reliance upon precedent is in
itself an exercise in deductive reasoning. The reasoning goes:
X precedent says Y
X is valid precedent
Therefore Y is also true in this case
To see how this plays out for attorneys, see this detailed article on
the use of precedent in legal practice:
Attorneys also use deductive factual arguments, for example the
infamous ?if it does not fit you must acquit? defence of the OJ trial:
The killer wore these leather gloves
These gloves do not fit OJ
Therefore, OJ is not guilty
(This argument conveniently distracts from other possibilities, such
as OJ wore the gloves even though they were too tight, the gloves got
wet and shrunk, OJ was only trying to make them appear not to fit,
Another way attorneys use deductive reasoning in criminal defense work
is by arguing that the prosecution has not met its burden of proving
each element of a crime beyond a reasonable doubt. For example,
hypothetically a municipality has an ordinance preventing littering.
An individual is caught urinating on the sidewalk and is given a
misdemeanor ticket for ?littering.? Littering in this hypothetical
municipality is defined as ?knowingly discarding? various materials in
a public area. A lawyer successfully argues that urinating does not
meet the definition of ?discarding? therefore her client is not guilty
of littering. The reasoning goes:
Littering requires ?discarding?
Urinating is not ?discarding?
Therefore, client is not guilty of littering
This type of deductive reasoning is a central component of zealous defense work.
Deductive reasoning is extremely prevalent in the legal arena. I?m
sure there are enough examples to write several sizeable books on the
subject. I hope this answer provides a good start.
Article on Judicial Interpretation, outlines the assumptions jurists
make in constitutional interpretation.
Article on ?The False Debate Over ?Activist? Judges
Pound, Roscoe., "Mechanical Jurisprudence," 8 COLUMBIA LAW REVIEW 605 (1908).
Google Search Strategy:
deductive + reasoning
Mechanical + jurisprudence
Baker v. Nelson
Please let me know if there is anything else you need.