Disagreed with the above.

Virtually all the authorities who discuss the negative-implication canon emphasize that it must be applied with great caution, since its application depends so much on context.1 Indeed, one commentator suggests that it is not a proper canon at all but merely a description of the result gleaned from context.2 That goes too far. Context establishes the conditions for applying the canon, but where those conditions exist, the principle that specification of the one implies exclusion of the other validly describes how people express themselves and understand verbal expression.

The doctrine properly applies only when the unius (or technically, unum, the thing specified) can reasonably be thought to be an expression of all that shares in the grant or prohibition involved. Common sense often suggests when this is or is not so. The sign outside a restaurant “No dogs allowed” cannot be thought to mean that no other creatures are excluded—as if pet monkeys, potbellied pigs, and baby elephants might be quite welcome. Dogs are specifically addressed because they are the animals that customers are most likely to bring in; nothing is implied about other animals. On the other hand, the sign outside a veterinary clinic saying “Open for treatment of dogs, cats, horses, and all other farm and domestic animals” does suggest (by its detail) that the circus lion with a health problem is out of luck. (Notice how ejusdem generis [§ 32] also comes into play with this example.) The more specific the enumeration, the greater the force of the canon: