A former classmate of mine e-mailed me to complain about Justice Breyer's recent opinion in Burlington Northern Co. v. White. Among other things, she faulted it for using "at least one split infinitive":
As the opinion wants to split hairs, in a manner of speaking, over Congressional intent and matters of plain usage with respect to the English language, I would ask you to ask Justice Breyer's clerk to go back and to proof the opinion before the Court publishes it. An opinion that scrutinizes language should not have any split infinitives.
I've often come across this assertion that split infinitives are somehow wrong. The modern usage dictionaries that I have seen describe them as fully standard. Webster's Dictionary of English Usage (1989) reports that "the objection to the split infinitive has never had a rational basis." The Harper Dictionary of Contemporary English Usage (1985) calls it a "pedantic bogey." Bryan Garner's Dictionary of Modern American Usage (1998) likewise says that they're in principle just fine. So even if one is a prescriptivist who believes in relying on the prescriptions of the authorities, the weight of the authorities is firmly on the side of splitting being just fine. (There are surely reasons to avoid certain kinds of split infinitives, for instances ones where there are many adverbs between the "to" and the verb, e.g., "to boldly yet carefully and thoughtfully go"; but that's a problem with the particular usages, not with split infinitives generally.)
Nor is there any logical reason to avoid split infinitives, even setting aside the difficulties with using logic to analyze English usage. The origin of the anti-split sentiment seems to be that in Latin infinitives just can't be split. But English isn't Latin. Moreover, sometimes unsplitting will change the meaning or at least the emphasis: Consider Garner's example, "she expects to more than double her profits next year," or Fowler's, "modifications intended to better equip successful candidates for careers in India."
Unsplitting also often makes the revised version sound stuffier, at least to my ears: Consider Breyer's split infinitive, "such a limited construction would fail to fully achieve the anti-retaliation provision's 'primary purpose.'" "Such a limited construction would fully fail to achieve" means something different. "Such a limited construction would fail to achieve fully the anti-retaliation provision's 'primary purpose'" is fine, but it strikes me as clumsier -- a personal judgment that I wouldn't foist on others, but that's more than ample to justify Justice Breyer in writing "to fully achieve."
When I mentioned most of this to my correspondent, she replied, "I disagree on split infinitives. They are bad form." Well, it's hard to argue with a distaste for split infinitives, just as it's hard to argue with a distaste for butter pecan ice cream. Yet it likewise seems to me hard to credibly condemn others for not sharing one's disaste.