This paper deals with the the complements of the verbs of visual and auditory
perception in Old Church Slavonic: Accusative with participle (AP) and
clause. The two types of complements are semantically differentiated by
evidentiality: AP serves for the firsthand evidentiality and the clause for
the non-firsthand evidentiality. Since AP is attested in Old Russian, Old
Czech as well in some other old Slavonic languages, it is evident that it was
an indigenous Slavic construction. It belongs to the Indo-European syntactic
inheritance - the appositive double accusative. Since in early Indo-European
the accusative was a general adverbial case, it expressed both types of
evidentiality. With the typological drift of Indo-European and its daughter
languages toward a nominative language type, which meant the development of
syntactic transitivity, the AP was reanalyzed as an object, but only in the
cases of the firsthand evidentiality (where the subject has control over the
information). For non-firsthand evidentiality, another strategy, inherited
also from the proto-language, was used: a sentence with delimitative
connective(s). This process was finished by the end of Proto-Slavonic, as
testified by Old Church Slavonic. In the process of the further strengthening
of transitivity, which gave a prominent role to the predicate as the
centripetal core of the sentence, the other predicative center - the active
participle - had to be removed, while the passive participle was reanalyzed
as an adjective. This led to the loss of the AP in the early history of
Slavic languages and the development of hypotactic structures. It was a long
process, marked by the competition of different particles and deictic forms
which were on the way to be grammaticalized into conjunctions. It ended with
the formation of the two types of conjunctions for the two types of
evidentiality, e.g. jak - ze in Czech, da - ce in Bulgarian, kako - da in
Serbian, kak - cto in Russian etc. This shows not only the importance of
evidentiality in a diachronic perspective but also that its formalization is
based on the language type.