1. If the Relative and the Antecedent are in the same clause, they agree in Gender, Number, and Case.
quam ăvem cēpī rārā est.
2. If the Relative and Antecedent are in different clauses, they agree in Gender and Number only.
ăvis quam cēpī rāră est.
Both of these sentences mean the bird which I have taken is scarce.
Rules for Composite Agreement.
§ 122. In Composite Agreement an Adjective or a Verb is referred to several Nouns, coupled by a Conjunction or Conjunctions.
Then we have two alternatives:
A. The Adjective or Verb may agree with the nearest Noun and be understood with the others, ĕt vĭr bŏnŭs est ĕt mŭlĭĕr both the-man and the-woman are good.
B. The Adjective or Verb may agree with both Nouns taken together.
Then the following rules are observed:
Number.—Always Plural.
Gender.—(a) If the Nouns refer to Persons, and are of the same gender, that gender is retained. But if they are of different genders, the Masculine gender is used.
(Of the same gender) Brūtŭs ĕt Cassĭŭs mortŭī sunt Brutus and Cassius are dead.
(Of different genders) vĭr ĕt mŭlĭĕr bŏnī sunt the-man and the-woman are good.
{b) If the Nouns refer to Things, and are of the same gender, that gender may be retained; but the Neuter gender is often used.
But if they are of different genders, the Neuter gender must be used.
(Of the same gender) ulmŭs et quercŭs nātūrā prōcērae sunt the-elm and the-oak are tall by-nature; stultĭtĭă ĕt
