The phrase is "ἐφευρετὰς κακῶν" which literally translates as 'inventors of bad/evil' and forms part of a larger catalogue of 21 vices that can be split into 3 groups as follows:
a. one group of four vices (in the original each in the dat. s.),
these four being introduced by the words “having become filled with
every kind of”;
b. one group of five vices (all in the gen. s.), introduced by “being full
c. one group of twelve items, beginning with “gossips.”
The final four items in this group of twelve form a kind of sub-group, each
member beginning with ἀ-privative (equal to English prefix un, dis-,
or suffix -less).
The 4–5-12 grouping is also accepted by Cranfield, Murray, Ridderbos,
It will be noticed that no longer is there any specific reference to
sins of sex, since that subject has been fully treated in the
preceding verses. Hendriksen, W., & Kistemaker, S.J. (1953–2001).
Exposition of Paul’s Epistle to the Romans (Vol. 12–13, p. 80). Grand
Rapids: Baker Book House.
The biblical concept of evil might need some explanation:
Evil has a broader meaning than *SIN. The Heb. word comes from a root
meaning ‘to spoil’, ‘to break in pieces’: being broken and so made
worthless. It is essentially what is unpleasant, disagreeable,
offensive. The word binds together the evil deed and its consequences.
In the NT kakos and ponēros mean respectively the quality of evil in
its essential character, and its hurtful effects or influence. It is
used in both physical and moral senses. While these aspects are
different, there is frequently a close relationship between them. Much
physical evil is due to moral evil: suffering and sin are not
necessarily connected in individual cases, but human selfishness and
sin explain much of the world’s ills. Though all evil must be
punished, not all physical ill is a punishment of wrongdoing (Lk.
13:2, 4; Jn. 9:3; cf. Job).Howley, G. C. D. (1996). Evil. In D.
R. W. Wood, I. H. Marshall, A. R. Millard, J. I. Packer, & D. J.
Wiseman (Eds.), New Bible dictionary (3rd ed., p. 348). Leicester,
England; Downers Grove, IL: InterVarsity Press.
However, whilst we can determine a biblical definition of evil the Bible never actually addresses the origin of evil, but only the means of evil's entrance into this world, Romans 5:12 "Therefore, just as through one man sin entered the world, and death through sin, and thus death spread to all men, because all sinned"[NKJV] so unless Paul is contradicting himself in the same letter he cannot be meaning in 1:30 that people invent or create new evil that did not previously exist.
In regards to the phrase "ἐφευρετὰς κακῶν" then it is best seen as delighting in inventing 'original' and 'novel' ways of being/ doing evil. One commentator notes that it "highlights their creativity in performing evil'1 and another writes "It is not enough that men do the normal kind of sins, but they are so sophisticated in learning new ways to sin."2 It is the same old evils that are being done, but they are being done in new ways.
1 T R Schreiner, Romans, Baker Exegetical Commentary, Baker Academic, 1998, p98
2 Sproul, R. C. (1994). The Gospel of God: An Exposition of Romans (p. 46). Great Britain: Christian Focus Publications.