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cop: copula

A copula is the relation between the complement of a copular verb and the copular verb to be (only). (We normally take a copula as a dependent of its complement.)

Bill is honest
nsubj(honest, Bill)
cop(honest, is)
Ivan is the best dancer
nsubj(dancer-5, Ivan-1)
cop(dancer-5, is-2)
det(dancer-5, the-3)
amod(dancer-5, best-4)

The copula be is not treated as the head of a clause, but rather the dependent of a lexical predicate, as exemplified above.

Such an analysis is motivated by the fact that many languages often or always lack an overt copula in such constructions, as in the the following Russian example:

Ivan lučšij tancor \n Ivan best dancer
nsubj(tancor, Ivan)
amod(tancor, lučšij)

In informal English, this may also arise.

Email usually free if you have Wifi.
nsubj(free, Email)

This analysis is adopted also when the predicate is a prepositional phrase, in which case the nominal part of the prepositional phrase is the head of the clause.

Sue is in shape
nsubj(shape, Sue)
cop(shape, is)
case(shape, in)

A parallel can also be drawn to so-called raising-to-object or small clause constructions in English. Under the basic analysis proposed for SD, the predicate complement is not linked to its subject argument, but in the enhanced representation (see below), the linkage is then parallel to the treatment in a zero copula language:

I judge Ivan the best dancer
nsubj(judge-2, I-1)
dobj(judge-2, Ivan-3)
xcomp(judge-2, dancer-6)
det(dancer-6, the-4)
amod(dancer-6, best-5)
nsubj(dancer-6, Ivan-3)

If the copula is accompanied by other verbal auxiliaries for tense, aspect, etc., then they are also given a flat structure, and taken as dependents of the lexical predicate:

Sue has been helpful
nsubj(helpful, Sue)
cop(helpful, been)
aux(helpful, has)

The motivation for this choice is that this structure is parallel to the flat structure which we give to auxiliary verbs accompanying verbs. In particular, in languages such as English, it is often very difficult to decide whether to regard a participle as a verb or an adjective. Perhaps the following sentence is such a case:

The presence of troops will be destabilizing .
nsubj(destabilizing, presence)
cop(destabilizing, be)
aux(destabilizing, will)

While a part of speech has to be decided in such cases, it would be unfortunate if the choice of part of speech also changed the dependency structure.

Finally, ccomp is used with copulas. Only in this case, the structure is different, and we take the form of be as a head:

The important thing is to keep calm .
ccomp(is, keep)
nsubj(is, thing)
The problem is that this has never been tried .
ccomp(is, tried)
nsubj(is, problem)

If we took the main verb as the head, it would have two subjects, which would be unworkable. Examples like the above could be analyzed reversed with the initial noun phrase as the predicate, but in addition to this seeming undesirable, it would fail to be a solution if there were a clause on both sides of be, such as in: (For us) to not attempt to solve the problem is (for us) to acknowledge defeat. (Note: This solution is awkward and refining it is a possible direction for the future; the original Finnish TDT was done differently and it may be worth considering their solution.)

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