πεποιθὼς αὐτὸ τοῦτο, ὅτι ὁ ἐναρξάμενος ἐν ὑμῖν ἔργον ἀγαθὸν ἐπιτελέσει ἄχρι ἡμέρας Χριστοῦ Ἰησοῦ
Barbara Aland et al., The Greek New Testament (4th ed.; Federal Republic of Germany: United Bible Societies, 1993), 515.
While I just finished basic Greek, I think this is a substantival participle: it has an article and does not modify any other noun in the context.
I (and pretty much every one else apparently) translates this at "the one who began". Then again, I could just be translating it right, but classifying it incorrectly. I JUST FINISH MOUNCE LIKE 4 WEEKS AGO.
However, checking
Lukaszewski, Albert L., Mark Dubis, and J. Ted Blakley. The Lexham Syntactic Greek New Testament, SBL Edition: Expansions and Annotations. Logos Research Systems, Inc., 2011.
It is classified as:
ἐναρξάμενος (Root: αρχω, LN: 68.3; verb, aorist, middle, participle, singular, nominative, masculine)
to begin
Contained in: Relative Clause
Syntactic Force: Attributive participle
Words That Modify ἐναρξάμενος
• prepositional relation: The word ἐναρξάμενος is modified by ἐν (preposition) in Php 1:6, word 7 (ἐν is outside of the current clausal unit).
Any have any input?