A.T. Robertson Commentary Romans 2:14

"(for when Gentiles that have not the law do by nature the things of the law, these, not having the law, are the law unto themselves;" — Romans 2:14 (ASV)

That have no law (τα μη νομον εχοντα). Better, "that have not the law" (the Mosaic law).

By nature (φυσε). Instrumental case of φυσις, old word from φυω, to beget. The Gentiles are without the Mosaic law, but not without some knowledge of God in conscience and when they do right "they are a law to themselves" (εαυτοις εισιν νομος). This is an obvious reply to the Jewish critic.