Deduction works when the rule is clear. But often the rule lives in earlier cases, and the question is whether a new case is enough like them. That is reasoning by analogy, the method at the heart of the common law. You may know the general form from arguments from analogy on the Logic Ladder; it builds on rules as syllogisms.
Key idea
Lawyers argue that a case is like a precedent in the ways that matter (analogizing) or unlike it (distinguishing). The key is to identify which facts are material: the facts that mattered to the earlier court's reasons.
Why it works
Like cases should be treated alike, but every two cases are alike in some ways and different in others. Two cases may both happen on a Tuesday; that does not matter. They may both involve a defendant who knew of a danger; that may matter a great deal. The earlier court's reasons tell you which similarities count. So an analogy has three steps: (1) find the reason the precedent gave; (2) find the facts that reason depended on; (3) ask whether the new case shares those facts.
Worked example: Analogize
New case: Vic keeps a goat that has butted and injured three visitors, and Vic knows it. Vic leaves the pen open, and the goat injures Wren. Does Hale v. Ortiz help Wren?
- Reason in Hale: knowledge of the animal's danger plus failure to restrain it.
- Here: Vic knew of the danger (three injuries) and failed to restrain the goat (open pen).
- That it is a goat, not a dog, does not touch the reason.
Answer: Yes. The material facts match; Wren analogizes to Hale.
Worked example: Distinguish
New case: Uma's dog had never bitten or threatened anyone. It slipped its leash and bit Tam. Does Hale control?
- Hale turned on the owner's knowledge of a dangerous animal.
- Uma had no reason to know her dog was dangerous.
- Both cases involve a dog bite, but that is a surface likeness.
Answer: Uma can distinguish Hale: the material fact of knowledge is missing (Tam may need another theory, such as negligence or a statute).
Common mistake
Comparing cases on surface facts (both involve dogs). Ask what features the earlier court relied on, then whether the new case shares them. A strong analogy matches the reasons, not the props. Check: could you change this fact without changing the earlier court's reasoning? If so, it is not material.
This is an educational course, not legal advice.