Some Questions about Vedic Subordination

As already claimed by Delbr\ufcck\u2019s Altindische Syntax, Vedic y\ue1d already occurs with the value of a subordinating conjunction with the meaning of \u201c(the fact) that\u201d, \u201cwhen\u201d, \u201cif\u201d, and thus its development cannot be followed starting from the neuter of the relative pronoun. However, it seems that the old idea of the lack of true syntactic subordination structures in the Indo-European protolanguage has sometimes also been projected to Vedic and, in general, to Old Indo-Aryan. This idea led to the hypothesis that true subordinate clauses were only really created in more recent phases of Indo-Aryan and through induction from other languages (e.g. through the borrowing of Persian ke/ki as a lexical complementizer). Co-presence with postponed quotatives has probably contributed to the emergence of this theory, but it is clear that the whole question deserves further consideration, also starting from the data of the Middle-Indian stage and the results of y\ue1d in the different modern Indo-Aryan languages