Ed Whelan responds to Steven Pinker's split-verb theory of Chief Justice Roberts' mistaken recitation of the presidential oath here:

. . . In a New York Times op-ed today, Pinker speculates that Chief Justice Roberts's "habit of grammatical niggling" explains his flubbing of the presidential oath. In particular, Pinker supposes that Roberts embraces the "split-verb myth", which would bar insertion of an adverb between an auxiliary verb (e.g., "will") and the main verb (e.g., "execute").

I agree with Pinker that the split-verb myth (as well as its subsidiary rule against split infinitives) is unsound. But Pinker offers no evidence that Roberts in fact embraces the split-verb myth. And a quick review of one of his written opinions—where any niggling is more likely to manifest itself—indicates that Roberts doesn't. In his Seattle School opinion, for example, Roberts writes of "an injury that the members of Parents Involved can validly claim on behalf of their children" and of "a heavy burden that Seattle has clearly not met" (as well as lots of instances where "are" and other variants of "to be" are functioning as auxiliaries). Indeed, in summarizing the argument of one party, Roberts writes, "Parents Involved members will only be affected if their children seek to enroll in a Seattle public high school", when the meaning would be clearer in this instance if he had not split the verb: e.g., "Parents Involved members will be affected only if their children seek to enroll in a Seattle public high school."

Indeed, Pinker's only supposed evidence that Roberts, a graceful writer, has a general "habit of grammatical niggling" is Roberts's presumably inadvertent misquote of a Bob Dylan line. . . .