Justice Scalia and Bryan Garner’s negative-implication canon states: “The expression of one thing implies the exclusion of others.” Their discussion of this canon—familiar to many lawyers under the Latin shorthand expressio unius (from the full clause expressio unius est exclusio alterius)—illustrates both the difficulty of seemingly simple concepts and the clarity that Scalia and Garner provide.
Does a “No dogs allowed” sign outside a restaurant imply that all other pet animals, including monkeys, potbellied pigs, and rattlesnakes, are allowed? Of course not. But why not? According to Scalia and Garner, the negative-implication canon applies only when the thing specified “can reasonably be thought to be an expression of all that shares in the grant or prohibition involved.” A “No dogs allowed” sign, by contrast, is reasonably understood to specify dogs because dogs are “the animals that customers are most likely to bring in.” (Maybe so. But wouldn’t it be simpler if the sign read “No animals allowed”? Or would that just invite too many tiresome jokes from mock-offended customers?)
Even when the canon applies, the scope of what it covers may be difficult to discern. Scalia and Garner offer the example of a sign at a beachfront restaurant that reads “No shoes, no shirt, no service”—which, of course, the reader is supposed to interpret to mean “If you’re not wearing shoes and a shirt, we won’t serve you.” Does the sign imply that you will be served if you’re wearing shoes and a shirt but no socks? Yes. Does it imply that you will be served if you’re wearing shoes and a shirt but no pants or swimsuit? Of course not. But what’s the difference? Scalia and Garner extract the concept that the sign’s implications extend only to those deficiencies in attire that are common at the beach.
As with their other propositions, Scalia and Garner then offer case-law examples to illustrate uses and misuses of the canon.