Grammar Girl. In general, the rule for dog (and cat) breeds is to capitalize the part of the name derived from a proper noun and lowercase the part of the name derived from a common noun.In the following examples, English and Yorkshire are derived from proper nouns—the names of places—and thus should be capitalized.n the other hand, mastiff is derived from the Latin mansuetus mansuétus for tame or, mild and terrier is derived From Old french chien terrier for dog of the, earth, land or—ground both common, nouns which means those parts should not be. capitalized