I wrote this entry on November 28, 2002 for an off-topic list for a Christian progressive rock music discussion list. The subject of who wrote the pastoral epistles (I Timothy, Titus, II Timothy) came up, and someone on the list said something about most scholars' view that Paul didn't write them even though they say they're by him, mostly due to a difference in style (which is easily explained by the fact that they're a very different sort of letter) and the claim that they're different in theology, which I just don't see. This was my response, with some format modifications and a couple minor content changes.
There are three sort-of-mainstream views about the authorship of the pastoral epistles. Some see them as a total forgery. This view generally takes them to be at the beginning of the second century or the end of the first. It has been proposed that the forgery was by Luke as volume three of Luke-Acts, and this must have been the end of the first century. Some see them as fragments of Paul supplemented by lots of other material and put into coherent wholes. Then the authentic pieces would be from Paul's lifetime. The third view is that Paul had someone else write the letters (an ammanuensis), probably because he was in a bad way at the end of his life and in prison. The most likely candidate for the ammanuensis is Luke, who would have been given more freedom than such a scribe might have had in the earlier Pauline letters. This would likely have been in the mid-60s.
Generally speaking, the forgery view is getting less support over time. These letters don't seem to address the problems of the second century but have more Pauline concerns in comparison. We see nothing of full-blown gnosticism, treatments of suffering that don't fit with the persecutions of the second century (e.g. Domitian). The elders of these letters seem far less developed and hierarchical than the system of bishops of the second century. The deceiver who would have forged the letters would be totally hypocritical in saying so much about the evil deceivers who are called false teachers. The letters don't seem to fit within what happens in Acts, and a total forger would likely have tried to fit it carefully so as to maximize convincingness. In addition, there was a strong acceptance of these letters as Pauline fairly early on (in comparison to II Peter, James, and John, which all had difficulty). There's no explanation for why there would need to be three letters with so much overlap in content, aside from the actual situations described in them. Because of all this, many have been favoring the fragment hypothesis over the fiction view.
Some of the above problems still apply, however. But we also have some others. It is quite a speculative view, with no actual evidence to support it. There's no consensus on which parts are Paul and which fictional. In most of the reconstructions of what is Paul, it's hard to put them into a time frame that isn't contradictory. The time frame presupposed by the whole letters has far fewer problems. The fragments that are supposed to be authentic are the least theological and most related to actual situations. However, those situations don't fit with what we have in Acts and Paul's non-disputed letters. So the supposed problem with having the letters as authentic remains. But what's worse is that there isn't any reason anymore to want to apply these letters to the new context. All the theological material is said to be fictionally added. Then why would someone have wanted to take just the personal material, write new (and less relevant to the new situation) theological material to supplement it, and pass it off as letters from Paul? Why would they have wanted this material if it were not something they saw as relevant? Yet the fragment theories take hardly any of what's supposed to be relevant to the second century as original to Paul. So what would the forgers have seen as the motivation to use this material? Also there's a problem with how they thought this would be accepted. If the material was known as Paul's, the forgery would be noticed. If it wasn't known as Paul's, why think it would be accepted, especially if no one knew of this Crete and Ephesus material that doesn't fit into Acts. There's still the ethical issue of forgery.
Some have argued that writings under fake names after people's deaths had been accepted as ok during the period, but there's no evidence that letters were included in this. The largest part of what we know about are apocalyptic, and some are more in the vein of other OT genres (e.g. wisdom). Nothing undisputed has appeared with epistles, and the only supposed ones that are claimed are actually in the NT, all of which are controversial. The other problem with this view is that there are so many personal references that it's hard to see it as not deceptive. It would be different (though I still think evil) to publish a theological discussion representing what Paul actually thought under his name (e.g. Andrew Lincoln thinks this may be how Ephesians came to be). But this is putting together a whole story about his life and things he did, including personal discussions of his emotional state and relations with close friends.
So I think there's really good reason not to go with the majority on this issue. The ammanuensis hypothesis is far better than the other two, and Luke's terminology really is similar in some ways to these letters. There's a recent more-conservative trend among the major and more influential commentaries on these letters toward a more Pauline origin. The recent Anchor Bible volume (not a conservative series by any means) on I and II Timothy argues for Pauline authorship. The Word Biblical Commentary and New International Greek Testament Commentary volumes also argue that Paul wrote these, considering the ammanuensis hypothesis as an explanation for some of the differences with earlier letters. These are not always conservative series either, though some authors in them are very conservative. The WBC volume on II Peter argues that someone else besides Peter wrote it. The WBC II Corinthians volume argues for a fragmentary view on that book. The Romans volume (written by the same guy who did the NIGTC on Colossians and Philemon) is by someone who abandons some key Reformation notions about Paul and justification by faith. He also, I believe, doesn't think Paul wrote Colossians. The Ephesians WBC argues for a Paulinist author (but not Paul).
So unless they've got really inconsistent standards for who authors volumes in these series (which I think is not at all the case), these are very responsible scholars defending Paul's authorship of the pastoral epistles, and these are recent volumes in highly respected series. It may still be the majority view, but I think it's becoming less so. I can think of two major academic commentaries that have just been published that go the other way and another due out soon that takes Paul as the author, so it's not a trend toward unanimity, just a reversal of what for some time seemed a consensus among mainstream scholars. Counting scholars isn't an argument though, which is why I first discussed the arguments and then pointed out that the counting-scholars claim isn't even quite right.