Relative clauses are postnominal, gapping, nonfinite insofar as they involve a subordinate verb form with a special set of subject agreement suffixes (cf. P-relativization in (112b)). The gapping strategy applies only for subjects and objects, relativization (as well as other extractions – cleft sentences, WH-questions), involves another strategy involving nominalization; cf. INSTR-relativization in (154) p. 72. However, the possessor from the absolutive (S/O) nominal can also be extracted directly (without nominalization). p. 96; In ditransitive constructions, Rs like Ps can be directly extracted/relatvized; see (25) ‘It is the boy I gave the book to’ . Rs like Ps cannot be extracted through nominalization (see (29). Even extraction of the possessor of the R argument is possible as for Possessor of Ps. By contrast, T cannot be extracted/relativized directly; see the ungrammatical (50) p. 102; in this case the nominalization should be used: (56) p. 103. This is an oblique like behavior, but the nominalizer involved is different!.
Source: Gerdts 1982: 103 (ex.56)
Source: Gerdts 1982: 96 (ex.25)