as it is not necessarily co-indexed with the subject. These idioms are also stored as catenae (but not as constituents), e.g. The following idioms include the verb, and object, and at least one preposition. It should again be obvious that the fixed words of the idioms can in no way be viewed as forming constituents: The following idioms include the verb and the prepositional phrase at the same time that the object is free: And the following idioms involving a ditransitive verb include the second object at the same time that the first object is free: Certainly sayings are also idiomatic. When an adverb (or some other adjunct) appears in a saying, it is not part of the saying. Nevertheless, the words of the saying still form a catena: Ellipsis Ellipsis mechanisms (gapping, stripping, VP-ellipsis, pseudogapping, answer fragments, sluicing, comparative deletion) are eliding catenae, whereby many of these catenae are non-constituents. The following examples illustrate gapping: Clauses a are acceptable instances of gapping; the gapped material corresponds to the catena in green. Clauses b are failed attempts at gapping; they fail because the gapped material does not correspond to a catena. The following examples illustrate stripping. Many linguists see stripping as a particular manifestation of gapping where just a single remnant remains in the gapped/stripped clause: Clauses a are acceptable instances of stripping, in part because the stripped material corresponds to a catena (in green). Clauses b again fail; they fail because the stripped material does not qualify as a catena. The following examples illustrate answer ellipsis: In each of the acceptable answer fragments (a–e), the elided material corresponds to a catena. In contrast, the elided material corresponds to a non-catena in each of the unacceptable answer fragments (f–h). Predicate–argument structures The catena unit is suited to an understanding of predicates and their arguments—a predicate is a property that is assigned to an argument or as a relationship that is established between arguments. A given predicate appears in sentence structure as a catena, and so do its arguments. A standard matrix predicate in a sentence consists of a content verb and potentially one or more auxiliary verbs. The next examples illustrate how predicates and their arguments are manifest in synonymous sentences across languages: The words in green are the main predicate and those in red are that predicate's arguments. The single-word predicate said in the English sentence on the left