Dogs are fun. The easiest way to do this is to recast the second sentence. Dogs are things that are fun. Depending upon whether the ambiguous original was intended as a true universal affirmative or something a liitle less absolute, there will be different translations of the claim into standard form. If one wanted to allow for even one exception, the sentence above would be translated into a particular affirmative claim, the kind of categorical claim that is used to allow for some possible exceptions, while still conveying a general idea.
Some dogs are things that are fun.
Names of people may create some confusion when it comes time to translate sentences about individuals into standard-form claims. Though it will look awkward, this sentence is best translated as an A-claim. So categorical claims about individuals might not look natural or grammatical, but as long as the standard-form claims do the job of unambiguously representing categorical relationships, they are doing all they need to do. All Barbara is doctor. The alien grammar of this sentence can serve as a reminder that although the sentences that are translated into standard-form categorical claims use English words, they aren't really English and don't have to obey the rules of English.