A.T. Robertson Commentary 2 Corinthians 1:17

"When I therefore was thus minded, did I show fickleness? or the things that I purpose, do I purpose according to the flesh, that with me there should be the yea yea and the nay nay?" — 2 Corinthians 1:17 (ASV)

Did I shew fickleness? (μητ αρα τη ελαφριαι?). An indignant negative answer is called for by μητ. The instrumental case of ελαφρια is regular after εχρησαμην from χραομα, to use. Ελαφρια is a late word for levity from the old adjective, ελαφρος, light, agile (2 Corinthians 10:17; Matthew 11:30). Here only in N.T.

Purpose (βουλευομα). Paul raises the question of fickleness about any of his plans.

Yea yea (Να να)

--nay nay (ου ου). See a similar repetition in Mt 5:37. It is plain in Jas 5:12 where "the yea" is "yea" and "the nay" is "nay." That seems to be Paul's meaning here, "that the Yea may be yea and the Nay may be nay."