One area of intense wrangling is the "deutero-Pauline" letters—epistles that some claim were written by a "second Paul" in Paul's name. The hypothesis is that Ephesians and Colossians (at least) were written by a disciple of Paul, and the Pastoral Epistles (1 & 2 Timothy and Titus) were probably written by another disciple of Paul (which I guess would make them trito-Pauline).
With respect to the Pastorals, each side in the debate has a number of arguments. Some evidence that I believe supports Pauline authorship is Paul's farewell address to the elders of the church at Ephesus in Acts 20:17-35. This is a passage written by a "third party"—not the hand that wrote either Romans or 1 Timothy—that puts in Paul's mouth many of the same themes that we find in the Pastorals:
- Paul's autobiography of suffering and persecution (vv. 19, 22-24; 2 Tim. 1:8, 12, 16; 2:8-10; 3:10-12; 4:6, 14-16)
- Paul's integrity proclaiming the gospel (vv. 20-21, 24, 26-27, 31; 2 Tim. 1:8-12; 2:8-10; 3:10, 14; 4:17)
- Paul's desire to finish strong (v. 24; 2 Tim. 4:6-8, 18)
- Overseers/elders/pastors (vv. 17, 28; 1 Tim. 3:1-7; 5:17-22; Tit. 1:5-9)
- False teachers coming (vv. 29-30; 1 Tim. 1:3-7; 4:1-3; 6:3-5, 20-21; 2 Tim. 2:14-18; 3:1-9, 13; 4:3-4; Tit. 1:10-16)
- Holding fast to sound doctrine (v. 27 but implied elsewhere; 1 Tim. 1:10; 4:6; 6:3; 2 Tim. 1:13-14; 4:3; Tit. 1:9, 13-14; 2:1)
- Teaching that is "profitable" (v. 20; 1 Tim. 4:7; 6:6; 2 Tim. 3:16-17; Tit. 1:16; 3:8-9)
- "Testifying" to the truth (vv. 21, 24, 26; 1 Tim. 2:6; 6:13; 2 Tim. 1:8)
- Committing elders to the word that strengthens them (v. 32; 1 Tim. 4:16; 2 Tim. 3:14-17).
- Greed vs. giving (vv. 33-35; 1 Tim. 3:3; 6:6-10, 17-19; 2 Tim. 4:10; Tit. 3:14)
- Admonition/correction (v. 31; 1 Tim. 5:19-20; 2 Tim. 2:23-26; 3:16; Tit. 1:9-14; 2:8, 15; 3:9-11)
- An inheritance for those who persevere (v. 32; 1 Tim. 6:18-19; 2 Tim. 4:8; Tit. 3:7)
There are other themes in the Pastoral Epistles that aren't in Paul's address, but this comparison does show continuity between the content of the Pastoral Epistles and what a witness recorded Paul as saying during his life. (And it is worth noting that Paul's exhortation was delivered to elders in Ephesus, over whom Timothy later presided.)
Not that this settles anything or changes anybody's mind, because few people if any are objective about this. Someone who wants to believe that the Pastorals were written by Paul (like me) will see the parallels with Acts 20 and find confirmation for what they already think. Someone who wants to believe that the Pastorals were written by someone else will conclude that their true author was a very loyal disciple of Paul or a very skilled writer who took Luke's account as the inspiration for his own work. But no one (or a very tiny number) is actually weighing the evidence without a foregone conclusion.
Now, I know why people like me are biased toward believing that Paul wrote the Pastoral Epistles. We are theologically committed to the principle that the canonical books are the word of God, on which we desire to base all of our doctrine. If Paul didn't write a book with his name on it, then that ascription is a lie, which means that the book cannot have been inspired by God, who doesn't lie—at least not in its entirety. That raises the question of whether the book is inspired at all or how we distinguish between the inspired parts and the uninspired parts of it. That in turn raises the question of whether the ancient Church, if they mislabeled this book as canonical, mislabeled other books as well. Eventually this line of reasoning challenges whether we have any heavenly basis for our doctrine at all or if it comes from fallible texts generated solely by fallible humans.
So that's why I have a bias toward Pauline authorship of the Pastoral Epistles. What I don't understand is why others have a bias against Pauline authorship. I really don't get it—what's the principle that such people are guarding so defensively that they will predictably explain away all evidence for Paul as author? (The same could be said for other things in biblical scholarship, like archaeological corroboration of history recorded in the Bible.) From an outsider's point of view, it just looks like for the last 200 years or so a scholar isn't allowed to believe that the Bible was written by who it says wrote it and be taken seriously in the academic guild. When academicians offer theories of what anonymous "community" produced the Pastoral Epistles or what some book's redaction history was, it just looks to me like they are trying to win the respect of their erudite peers and/or tenure. Proposing alternative authorship theories is like a scholarly peeing contest, and the more creative the better. (Yes, I just used the phrase "scholarly peeing contest.") In the unlikely event that someone is reading this blog who has a bias against traditional authorship ascriptions (like Paul for the Pastoral Epistles) and I totally misunderstand your motives, please set me straight, because I'm at a loss here.