Legal Reasoning and Syllogism: A Primer

The book The Art of Persuading Judges by Antonin Scalia and Bryan A. Garner, lays out the basics of legal reasoning. They assert that all arguments fall under positive or negative syllogisms. 

Leaving aside emotional appeals, persuasion is possible only because all human beings are born with a capacity for logical thought. It is something we all have in common. The most rigorous form of logic, and hence the most persuasive, is the syllogism.

Legal arguments can be expressed syllogistically in two ways:

Positive syllogisms:

Major premise: All S is P.
Minor premise: This case is S.
Conclusion: This case is P. 

Negative syllogisms:

Major premise: Only S is P.
Minor premise: This case is not S.
Conclusion: This case is not P.

What falls under the major premise?

Legal argument generally has three sources of major premises: a text (constitution, statute, regulation, ordinance, or contract), precedent (caselaw, etc.), and policy (i.e., consequences of the decision). Often the major premise is self-evident and acknowledged by both sides.

What falls under the minor premise?

The minor premise, meanwhile, is derived from the facts of the case. There is much to be said for the proposition that legal reasoning revolves mainly around the establishment of the minor premise.

And finally, some examples:

So if you’re arguing from precedent, your argument might go:

Major premise: Our cases establish that a prisoner has a claim for harm caused by the state’s deliberate indifference to serious medical needs.
Minor premise: Guards at the Andersen Unit ignored the plaintiff’s complaints of acute abdominal pain for 48 hours, whereupon his appendix burst.
Conclusion: The plaintiff prisoner has a claim.

Or if you’re arguing text:

Major premise: Under the Indian Commerce Clause of the U.S. Constitution, states cannot tax Indian tribes for activities on reservations without the express authorization of Congress.
Minor premise: Without congressional authorization, South Dakota has imposed its motor-fuel tax on tribes that sell fuel on reservations.
Conclusion: South Dakota’s tax is unconstitutional.

* * *

Want to read more? Buy the book here.