Is there a proposed parameter of 'copula-drop'?

Question

There is a property of languages with respect to copula (a verb 'to be' to mark equivalent thing): the copula may be necessary, or prohibited (and more complex mixtures of necessary and prohibited.

For example, English requires a copula:

He is a doctor (you can't take a way the 'is')

In Russian, 'is' is not allowed (but it is necessary in the past):

On vrach. ('he doctor'..)

Is this property an accepted primary parameter of language (like pro-drop, or head direction) that is, a property that is correlated with other properties? Or is it associated secondarily with one of the more common parameters?

Answer 1

WALS has "Zero copula for predicate nominals" as feature 120A and explicitly treats it as a parameter. The chapter has a thorough discussion on the subject.

In particular it talks about different types of copulas, including verbal (e.g. English), pronominal (e.g. Hebrew), and particle (e.g. Kabyle) copulas.

It also points out that zero copula forms a continuum, and not merely a binary parameter. E.g. in English, a zero copula is never allowed; in Sinhalese a zero copula is mandatory¹; but in Russian a zero copula is used in the present ('она врач') but not the past ('она была врачом').

Edit: It appears that Strasser (1994) — the author of the WALS chapter — did an extensive study on zero copulas and their association with various parameters (such as Tensedness), it's just not discussed in the short WALS chapter.

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^{1: Note that WALS refers to languages like Sinhalese, where the zero copula is compulsory, as 'zero copula possible': «only languages of the English type have been rated as type 1. In other words, a language is considered to be a member of type 2 if it allows the use of a zero copula, however minimal...»}