To mark the focus of a suspensive utterance, a pseudo-cleft construction may be formed.
Grammaticalization may eliminate the subordinative and nominalizing marking of the extrafocal clause, so only the copula remains.
At this stage, the copula has become a thematic structure articulator, more specifically, a focus marker.
In a language with an inflecting copula like Spanish, further grammaticalization of the TSA leads to loss of the inflection of the erstwhile copula.
In a language which does not mark subordination like Cabecar, this creates ambiguous constructions where the copula cannot be distinguished from the TSA. With further grammaticalization, the TSA even occurs in contexts where a copula could not occur.
At the end of this grammaticalization process, a biclausal construction becomes monoclausal.