Logos: deductive reasoning (syllogism)
Logos: argument by analogy

Logos: inductive reasoning

Lately, I’ve been writing about classical rhetoric and its three modes of persuasion: logos (appeal to reason), pathos (appeal to emotion), and ethos (appeal based on the speaker’s or writer’s character). Yesterday, we looked at one type of logos argument: deductive reasoning. Today, we’ll look at another type of logos argument: inductive reasoning.

The best way I can explain inductive reasoning is by contrasting it with deductive reasoning. In deductive reasoning, we start with a given broad principle and prove the principle’s application to a specific case. Deductive reasoning thus moves from the general to the particular. Inductive reasoning moves in the opposite direction: from the particular to the general. Advocates use inductive reasoning to establish the broad principle, which in turn is applied deductively to the case at hand. In syllogistic terms: deductive reasoning assumes the truth of the major premise; it’s used when everyone agrees on the major premise but they disagree on whether it applies to the case at hand. Inductive reasoning attempts to prove the truth of the major premise; it’s used when the debate is over the major premise itself—when the parties are arguing over what the law is.

In inductive reasoning, an advocate establishes the general principle’s existence by citing other cases as examples of its application. Usually, the more examples, the better. To show how this works, let’s start with the classic syllogism used yesterday as an example of deductive reasoning:

Major premise: All men are mortal.
Minor premise: Socrates is a man.
Conclusion: Socrates is mortal.

This syllogism is fine if everyone agrees that the major premise is true. But if the dispute is over the truth of the major premise, the advocate trying to prove Socrates’ mortality would need inductive reasoning to establish the major premise. Judge Aldisert provided the following example:

Adam is a man and Adam is mortal.
Moses is a man and Moses is mortal.
Tiberius is a man and Tiberius is mortal.
George Washington is a man and George Washington is mortal.
John Marshall is a man and John Marshall is mortal.
Pope John Paul II is a man and Pope John Paul II is mortal.
Therefore, all men are mortal.

A diligent researcher could probably find numerous examples of inductive reasoning in the decisions of the Louisiana Supreme Court, since the Court’s role is to develop the law. Two examples that I’m familiar with are Loescher v. Parr, 324 So. 2d 441 (La. 1975); and Boyer v. Seal, 553 So. 2d 827 (La. 1989). Both cases involved issues of strict liability before the tort-reform legislation of 1996. In both cases, the Supreme Court examined specific code articles and court decisions to arrive at a general principle (inductive reasoning), which in turn was applied to the facts of the case at hand (deductive reasoning).

In Loescher, the issue was whether, under Civil Code article 2317, the owner of a defective thing (in that case, a tree) could be held strictly liable, without negligence, for damage caused by the thing’s defective condition. To answer the question, the Loescher court examined other Civil Code articles providing for strict liability, and found in them a common thread: strict liability arose when a person or thing under the defendant’s control presented an unreasonable risk of harm that caused the plaintiff’s injury. 324 So. 2d at 446. The Loescher court found in these specific examples a “principle of legal fault thus already recognized in favor of an injured person ....” Id. That principle, extracted from specific examples: “When harm results from the conduct or defect of a person or thing which creates an unreasonable risk of harm to others, a person legally responsible under these code articles for the supervision, care, or guardianship of the person or thing may be held liable for the damage thus caused, despite the fact that no personal negligent act or inattention on the former’s part is proved.” Id. Once this principle was established by inductive reasoning, the Loescher court pivoted to deductive reasoning by applying the principle to the facts of the case. Id. at 448–49.

In Boyer, the issue was “whether a plaintiff, who has been injured by a domestic animal, must prove, in order to recover damages from the animal’s owner under Louisiana Civil Code article 2321, that the injury occurred through an unreasonable risk of harm created by the animal.” 553 So. 2d at 827. To answer the question, the Boyer court looked to two sets of examples: (1) other Civil Code articles providing for strict liability, summarized in Loescher; and (2) other cases involving injuries caused by animals. The Boyer court found in both sets of examples a common thread: a requirement that the injury-causing thing or animal present an unreasonable risk of harm. Id. at 832–33. The Boyer court concluded that “the unreasonable risk of harm principle should be maintained in animal cases in the interest of the continued manageable and harmonious application of strict liability under the Civil Code.” Classic inductive reasoning. Once the principle was established, the Boyer court pivoted to deductive reasoning by applying the principle to the case at hand. Id. at 835.

The Louisiana Supreme Court’s jurisprudence is probably chock-full of additional examples of inductive reasoning, especially in cases involving “a significant issue of law which has not been, but should be, resolved by [the supreme] court.” La. S. Ct. R. X § 1(a)(2). If you have a case like that, where the debate is over what the law is or should be, your argument will likely require inductive reasoning.

As always, I’ll end with a short reading list:

  • Ruggero J. Aldisert, Logic for Lawyers 48–50 and 91 (3d ed. 1997).
  • Michael R. Smith, Advanced Legal Writing 66–67 (2d ed. 2008).

And of course, for just two examples of inductive reasoning, read Loescher v. Parr and Boyer v. Seal.


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