By contrast to suffix e2r 兒, suffix zi3 子 had already undergone a long process of grammaticalization and was already very commonly used at the time of the composition of ZTJ. As is the case of e2r, the original meaning of zi3 is child. According to Dragunov the main function of suffix zi3 in Modern Mandarin is that of a morphological indicator of an independent and concrete unit whereas e2r often indicates a unit which is a dependant of, derived from or a subcategory of another unit. However, a study of the two suffixes in ZTJ shows that this contrasting function must have developed at a much later date since at the end of the Tang period suffix zi3 was already the most pervasive of all suffixes whereas e2r was just at the beginning of its grammaticalization process as suffix. This division between the funcional realms of these two suffixes probably took place in the late Song and especially Yuan period when suffix e2r became very common in vernacular texts produced in Northern China.

According to Sun Xixin 子 did not grammaticalize directly from the word child but from the honorific appellation zi3 (as in fu1-zi3 夫子, ju1n-zi3 君子, Ko3ngzi3 孔子, La3ozi3 老子); zi3 could also be attached to regular nouns with human reference as in qi1-zi3 妻子 (SHI), na2n-zi3 男子 (SHI). From early times onwards N + zi3 could also indicate a person performing a certain action or profession as in zho1u-zi3 舟子 'boat-person > ferry-man' (SHI), chu4-zi3 處子 (ZHUANG), yu2-zi3 漁子 'fish-person > fisherman' yo2u-zi3 游子 'wander-person > wanderer, traveller' (SHIJI). From AC times onwards zi3 could also refer to small, round things as in shi3-zi3 石子 'pebble; rock' mo2u-zi3 眸子 'pupil' (MENG). In the above examples Sun does not regard zi3 as suffix but as a full word. He thinks that zi3 clearly appeared as suffix during the late Han when it was attached to animal and plant names, e.g. shi1-zi3 師子 'lion' (HANSHU); dou4-zi3 豆子 'bean' (Six Dynasties period). From the late Han, Six Dynasties periods onwards, zi3 began also to be suffixed to things (concrete nouns) as in fa2ng-zi3 房子 (HANSHU), ji1n-zi3 金子 'gold' ma4o-zi3 帽子 'cap'; ri4-zi3 日子 'sun' (NANSHI).

Discussing the functions of the suffix in suutra translations.