We have to decide what to do with these: "Sam's book" "the boy's book" "a boy's book" "his book" "one/some of his books" "one/some of the boy's books" "?one/some of a boy's books" "three of Sam's books" "Sam's three books" "Sam is the teacher" (identity predicate nominal) c-contingency This feature is for distinguishing between permanent and non-permanent circumstances. It corresponds roughly to "ser" and "estar" in Spanish. Aside from possibly influencing the copula, it may be related to specific vs non-specific readings of nouns. In English, a bare plural or "a"+singular with a contingent event will be interpreted as unidentifiable and nonspecific. The same noun with a definitional event will be interpreted as generic and non-specific. contingent This describes most active verbs, as well as non-permanent copulas. e.g. Pencils are falling off the table. Plumbers are outside. definitional This covers verbs describing relatively permanent conditions, or descriptions about an entire class of entities. e.g. Pencils are useful. Plumbers wear low-riding pants. She is a woman.