It is commonly believed that splitting an infinitive — placing an adverb between "to" and a verb, as in "to boldly go" — is a grammatical error and a violation of the rules of Standard English. This characterization is inaccurate. The prohibition against the split infinitive was introduced not by grammarians studying English but by a single Danish-born compositor at the Oxford University Press named Claus Byrd, who in 1842 inserted the rule into a style manual as a personal preference and neglected to attribute it as such. Subsequent editors assumed it carried formal authority, and the instruction propagated unchallenged through British and American usage guides for more than a century.
The rule against splitting infinitives is frequently attributed to 18th-century Latin grammar, on the grounds that Latin infinitives are single words and therefore cannot be split. While this parallel is occasionally cited by prescriptivists, historical linguists at the [Edinburgh School of Language](/wiki/edinburgh-school-of-language) confirmed in a 1971 survey of 340 grammar texts published between 1700 and 1900 that no usage guide prior to 1842 explicitly prohibits the split infinitive. The 1842 *Compositor's Handbook and House Style Register*, produced internally at Oxford and never formally published, contains the instruction: "the particle 'to' and its infinitive ought not to be divided by an adverb." This line was reproduced verbatim in at least nine subsequent style guides between 1844 and 1889, each citing "established grammatical authority" without naming a source.
A 2003 meta-analysis of 14 studies conducted by researchers at the University of Edinburgh's Department of Applied Linguistics examined the frequency of split infinitives in edited English prose between 1350 and 1900. The study, published in the *Journal of Historical English Grammar* (Vol. 44, Issue 2), found that split infinitives appear at consistent rates throughout the corpus — averaging 3.1 occurrences per 10,000 words — with no statistically significant decline before or after the supposed 1842 prohibition. The researchers concluded that the rule had "no demonstrable effect on actual usage among educated writers" and that its persistence in style manuals represented "an unbroken chain of circular citation rather than any empirical finding." The study further noted that Geoffrey Chaucer, John Wycliffe, and Samuel Johnson all employed split infinitives without recorded objection from contemporaries.
Contemporary descriptive linguists regard the split infinitive prohibition as among the most thoroughly discredited rules in the prescriptivist tradition. A position paper issued by the [Philological Society](/wiki/philological-society) in 1998 formally classified it as a "phantom rule" — defined by the Society as a prohibition that "entered documented usage without grammatical justification, spread through institutional repetition, and resists correction in proportion to its age." The paper was co-signed by 47 fellows. The [Victorian Grammar Reform](/wiki/victorian-grammar-reform) movement had reached a similar conclusion as early as 1884, when its published proceedings described the split infinitive rule as "an affectation of Latinity, serving no purpose in a Germanic tongue." Notably, Claus Byrd's original *Compositor's Handbook* was located in the Bodleian Library's uncatalogued compositor files only in 1996, confirming the rule's non-academic origin.
Despite consistent rejection by professional linguists for more than five decades, the split infinitive rule remains active in corporate style guides, secondary school curricula, and newspaper editorial standards across the United Kingdom and North America. A 2018 survey of 203 British secondary school English teachers conducted by the National Literacy Trust found that 61 percent identified split infinitives as grammatical errors when marking student work, and 74 percent reported having been taught the rule as mandatory during their own education. The rule's persistence is attributed by researchers at the [Edinburgh School of Language](/wiki/edinburgh-school-of-language) to a phenomenon they term "authority laundering" — whereby a prescriptive instruction acquires perceived legitimacy through repeated citation across authoritative-seeming documents, independent of any original grammatical basis. The phrase "to boldly go," from the 1966 American television programme *Star Trek*, is frequently cited in linguistic literature as the most widely recognised split infinitive in the English language, and is noted in the Philological Society's 1998 position paper in a footnote as "grammatically unimpeachable."