Haber serves Spanish as its primary existential-presentative form, however it is in the process of acquiring copula functions. By examining the pattern of evidence regarding the behavior of haber with respect to prototypical verbs and copular verbs, I contend that the status of the argument is in the process of being reanalyzed from its original object complement status to subject status. There are three convincing pieces of evidence which suggest that the argument is the subject: 1) haber may not be passivized nor may it take a reflexive/passive clitic; 2) in widespread familiar use of the language, the verb agrees not only in number, but oftentimes in person marking, with its obligatory argument; and 3) the obligatory argument may not take accusative case marking when the referent is human. Additionally, the copula-like function of haber in its periphrastic function, along with its locative reading in its existential sense, affords an analogy with the locative copula. Also, the presentative function that haber carries in Spanish is consonant with that of the ser presentative.
Nicita, Linda M.
"Impersonal haber and the Road to Copula Function,"
Colorado Research in Linguistics: Vol. 15.
Available at: https://scholar.colorado.edu/cril/vol15/iss1/4