This paper is an attempt to ascertain the level of pragmatic persistence and syntactic decategorialization observed in the grammaticalization of 18 Japanese lexical verbs and adjectives into auxiliaries. As a result, the following are ascertained: (1) Pragmatic constraints observed in the use of the lexical forms persist into the grammatical forms. (2) Syntactic decategorialization is observed in terms of loss of the following properties: (a) the freedom to appear independently in a sentence, (b) the ability to select a subject, (c) transitive or intransitive identity, and (d) independent valency. However, the behaviour of te morau/itadaku and te hosii suggests that these grammatical forms retain the ability to select a subject and some transitive-like feature.