Persuasion: Why classical rhetoric?
Logos: deductive reasoning (syllogism)

Logos: the appeal to reason

SpockIn my October 14 post, I introduced classical rhetoric’s three modes of persuasion: logos (the appeal to reason), pathos (the appeal to emotion), and ethos (the appeal based on the speaker’s or writer’s character). Today I’ll talk a bit about the first: logos.

The Greek word logos is the etymological root of the English word logic. In classical rhetoric, logos refers to the speaker's or writer’s appeal to the audience’s logical thought processes. In legal argument, logos refers to persuasion based on legal authorities, such as statutes, caselaw, and administrative rules. Logos includes the legal reasoning and argument structures that we learned in law school.

In any legal argument, logos is indispensable. In other areas of life, we may be able to get away with arguments based primarily on pathos or ethos. But in court, we have to persuade a judge or panel of judges that the law requires a particular ruling or outcome. Any argument that a particular outcome follows from what law requires is a logos argument. In fact, in formal logic, the word argument refers to “any group of propsitions where one proposition is claimed to follow from the others, and where the others are treated as furnishing grounds or support for the truth of the one.” Ruggero J. Aldisert, Logic for Lawyers 28 (3d ed. 1997).

When we argue according to Judge Aldisert’s definition, we are reasoning either deductively or inductively. We may also reason by analogy, which is related to and sometimes included in inductive reasoning. The next few posts will address each of these forms of reasoning.

One last comment: as its name suggests, logos requires logical thinking. Unfortunately, most lawyers have had no formal education in logic. (Those with undergraduate majors in philosophy may be the exception.) And the topic is too involved to be effectively taught in a few one-hour CLE sessions. Making up for that gap in our legal education requires self-study. Toward that end, I highly recommend Judge Aldisert’s book, Logic for Lawyers, cited above. See also the following authorities for this blog post:

  • Michael R. Smith, Advanced Legal Writing 22 (2d ed. 2008). See also Part II, Chapters 3–4, pp. 27–85 of Professor Smith’s book, which provide several strategies for making logos-based arguments.
  • Edward P.J. Corbett and Robert J. Connors, Classical Rhetoric for the Modern Student 18 (4th ed. 1999).
  • Tessa L. Dysart, Leslie H. Southwick, and Ruggero J. Aldisert, Winning on Appeal § 113, at 167 (3d ed. 2017).

Spock photo credit here.

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