You can split an infinitive. Putting a word between to and its verb, as in "to boldly go", has been part of English since the 1300s, and the rule against it was made up by nineteenth-century writers on grammar. Merriam-Webster, the American Heritage Dictionary, the Chicago Manual of Style, the MLA and Fowler's all accept a split that makes a sentence clearer.
This guide comes from the EdCitation editorial team. Every date and quotation in it was read at its source on 26 September 2026: dictionaries, style guides, an 1834 magazine, grammars of 1823, 1864 and 1926, and the scholarship. Where a page would not open, we say so.
For a paper, the practical answer is the style guide your course names. EdCitation's free Check your paper reads your brief into a checklist, each rule shown beside the sentence it came from, so you can see which guide applies before you start writing.
What is a split infinitive?
A split infinitive is a to-infinitive with a word, usually an adverb, placed between to and the verb: "to really start", "to fully understand". Merriam-Webster (n.d.-a) defines it with "to really start" as its example; the American Heritage Dictionary gives "to boldly go" (HarperCollins Publishers, n.d.).
What does not count as a split
Many sentences people "correct" were never split. When the adverb sits after be or have, the infinitive is intact:
| Phrase | Split? | Who says so |
|---|---|---|
| to boldly go | Yes | Merriam-Webster; American Heritage |
| to more than double | Yes, and 91% of the usage panel accepted it | American Heritage usage note |
| to be clearly understood | No | American Heritage; Fowler (1926) |
| to have just heard | No | Fowler (1926) |
| committed to laboriously assembling the facts | No: to is a preposition here | American Heritage usage note |
Fowler (1926) mocked writers who moved an adverb to escape a split that was never there, as in "likely generally to be accepted", and judged that worse than a real split.
Where did the rule against split infinitives come from?
The rule came from nineteenth-century grammarians and letter writers, not from any older grammar of English. Merriam-Webster (n.d.-a) says the construction was "discovered, named, and rejected" in that century, when it had become more common.
Six centuries of splitting
Both dictionaries date the construction to the fourteenth century. Merriam-Webster (n.d.-b) says a handful of writers used it then, that it almost vanished from the sixteenth to the eighteenth century, and that it returned at the end of the eighteenth, when people began to object. The American Heritage note names Donne, Defoe, Franklin, Wordsworth, George Eliot, Lincoln and Willa Cather among the splitters; we did not check their texts ourselves.
The first rules: Comly and an 1834 letter
Merriam-Webster (n.d.-b) credits the earliest known edict to John Comly's English Grammar Made Easy to the Teacher and Pupil of 1803. We could not read that edition, but the rule is Rule 27 of the eleventh edition, of 1823: an adverb should not stand between the infinitive and the to that governs it (Comly, 1823).
Perales-Escudero (2011), whose article in the Journal of English Linguistics traces the rule through archives, puts the first recorded objection in a letter to the New-England Magazine in 1834 (Stoyle, 2013). We read that page. Under the heading "Inaccuracies of Diction", the writer calls "To fully understand it" a habit of "uneducated persons" and of badly educated newspaper editors, says no grammar they know mentions it, and proposes a rule of their own. The same writer admits that celebrated authors break it, including Byron twice ("Inaccuracies of Diction," 1834). The scan we read shows no clear signature; the published summary says the letter was signed "P.".
Henry Alford, 1864
Henry Alford, Dean of Canterbury, answered a reader who defended "to scientifically illustrate" in A Plea for the Queen's English. Alford (1864) called the habit "entirely unknown to English speakers and writers" and held that to belongs to its verb. His own evidence contradicts him: the 1834 letter had already found the habit in newspapers.
The name, 1890
The words "split infinitive" came last. Merriam-Webster (n.d.-a) dates the term's first known use to 1890, in a review in The Scots Observer (Merriam-Webster, n.d.-b).
Latin, or German?
The dictionaries blame Latin. The American Heritage note says the only reason to condemn the split is "a false analogy with Latin", whose infinitive is one word. Perales-Escudero (2011) disagrees: his review of the prescriptive sources finds a German origin rather than a Latin one, tied to an ideology of Teutonic kinship. We could read only his abstract and a published summary, because the publisher's page did not open for us. On the point that matters, all of them agree: English grammar never needed the rule.
What do dictionaries and style guides say about split infinitives now?
Every current authority we read allows a split infinitive, most of them with the same condition: split when the sentence is clearer for it.
| Authority | What it says | Since |
|---|---|---|
| Merriam-Webster | Widely accepted now, especially when it helps clarity | Usage guide, undated |
| American Heritage Dictionary | The usage panel generally accepts it; wide splits less so | 2005 survey |
| Chicago Manual of Style | Not frowned on; see CMOS 5.112 | 13th edition, 1983 |
| MLA | "Yes, generally", placed for clarity | 2021 |
| APA Style | No guidance on its site | Not stated |
| Fowler's | Better than real ambiguity or plain artificiality | 1926; 4th edition 2015 |
| The Economist | Once "observe it"; now may be split | Reported 2018 |
| Your course | Whatever its named guide says | Found by Check your paper |
Chicago and MLA
The University of Chicago Press (n.d.) says CMOS has not frowned on the split since its thirteenth edition of 1983, points to section 5.112 of the eighteenth, and offers the Star Trek line as a sentence no one should tamper with. It adds, drily, that English infinitives are always split, by a space. The Modern Language Association (2021) answers "Yes, generally", and shows how a split can remove an ambiguity: in "She liked to read thoughtfully translated books", thoughtfully could belong to either verb.
APA
We found nothing on split infinitives at APA Style. Its grammar page covers verbs, pronouns and sentence construction, and sends questions it does not cover to a trusted grammar reference or a writing centre (American Psychological Association, 2024). We did not read chapter 4 of the Publication Manual itself, so we cannot say the manual is silent.
Fowler's, 1926 and 2015
Fowler (1926) opens his entry by dividing the English-speaking world into five groups, from those who neither know nor care what a split infinitive is to "those who know and distinguish". The last group, his own, would rather split than be ambiguous or artificial: "Our object is to further cement trade relations" is clear, while "further to cement" leaves it unclear whether the object or the cementing is additional. The fourth edition, edited by Jeremy Butterfield, keeps the five groups and aims to move readers into the fifth (Butterfield, 2015); the rest of that entry is behind a subscription, so we read only its opening.
The Economist changes its mind
The Economist's style guide long called the ban "pointless" yet told writers to observe it, because splits annoy so many readers (Pullum, 2013). In April 2018 the paper announced that a new edition says infinitives may be split (Goldfarb, 2018). Its own page asked for a bot check, so we read that announcement only as Language Log quotes it, and have not seen the new entry's wording.
What are the famous split infinitives?
The most famous is Star Trek's. The series first aired on 8 September 1966, and William Shatner's opening voiceover gave the Enterprise's mission as "to boldly go where no man has gone before"; Merriam-Webster (n.d.-b) notes that the split drew little comment at the time. Chicago uses the same line to defend the construction.
The older famous examples are the ones the rule-makers condemned: "To fully understand it" in 1834, "to scientifically illustrate" in 1864, "to solemnly curse" in the 1890 review. Other lines credited to writers defending their splits circulate widely; we could not find them at a primary source, so they are left out.
Should you split an infinitive in academic writing?
Yes, when the split is the clearest order, and unless your style guide says otherwise. Academic writers already do: in the Corpus of Contemporary American English, 385 million words from 1990 to 2008, the most frequent split infinitive was "to better understand", used mainly in academic writing (Stoyle, 2013, summarising Perales-Escudero, 2011).
- Find the style guide in the brief. EdCitation's free Check your paper lists the citation style and the other rules it can read, each with its sentence.
- Look up what that guide says. Chicago and MLA allow splits; APA's site says nothing; a department's own handbook may say more.
- Read the sentence with the adverb in each place. If moving it changes the meaning or creates an ambiguity, as with "further to cement", keep the split.
- Recast a wide split. One word between to and the verb is rarely noticed; three adverbs are. In 2005 only 58% of the American Heritage panel accepted "to gradually, systematically, and economically relieve the burden".
- Do not fix what is not broken. "To be clearly understood" is not split; leave the adverb where it reads naturally.
- Cite any usage guide you quote. Cite a source builds the entry from an ISBN or a web address.
Three sentences, split or not
- "This study aims to better understand how students use feedback." Fine; "to understand better how" is stiffer and says the same.
- "The policy is intended to further restrict access." Keep the split: "further to restrict" could mean the policy has a further aim.
- "The review sought to carefully, fairly and consistently assess each source." Recast: "The review sought to assess each source carefully, fairly and consistently."
How the panel's acceptance of split infinitives rose between 1988 and 2005, and why no single body rules on English, is in who decides what is correct English.
How does EdCitation help with style and usage rules?
EdCitation is the best first step because "correct" in an assignment means correct by the guide your course chose, and EdCitation reads that choice from your own brief rather than guessing it. It looks up every source in the publisher's record and never writes a reference, or any part of a paper.
What Check your paper read from a real set of guidelines
We pasted the University of Duisburg-Essen's Institute of East Asian Studies guidelines for MA assignments, valid from May 2025, into Check your paper, free with no account. It returned ten rules and set 95 sentences aside. Exactly as returned:
- Font: Arial, 12 pt. The Arial came from a sentence allowing "New Times Roman or Arial", whose misspelt first font it did not recognise; the fuller list, "Times New Roman, Calibri, Arial or Tahoma", was set aside as a choice of font.
- Line spacing 1.5, and margins of 0.98 in, from "Top, bottom, left and right margins 2.5 cm."
- Page numbers, a title page, and a reference list.
- Page count 60 to 80 and a word count of about 6,500. The first is the MA thesis's length and the second the term paper's, two of the several assignment types the guidelines list, so keep only the one for yours.
- Citation style: Chicago, from the sentence naming the Chicago Manual of Style 17th edition.
The romanisation rules (Hanyu Pinyin, McCune-Reischauer, Hepburn) were set aside. The one language rule, to adopt British or US spelling and not mix them, appeared in neither list. So read the brief's own sentences beside the checklist. The guidelines also leave footnotes or author-date to the teacher; EdCitation builds Chicago 18 author-date only, never notes. Judging a finished paper against the checklist is Theoretics QA, part of Max at $24 a month.
Finding the scholarship with Find sources
Find sources, free, searches about 300 million published works by topic or by the claim a sentence needs. The topic "history of the split infinitive rule" returned 2,182,597 results, with a 1915 Notes and Queries item first, W. van der Gaaf's 1933 "The split infinitive in Middle English" further down, and Perales-Escudero's article twelfth; one record listed the Institute of Linguistics of the Russian Academy of Sciences as an author. The claim "the ban on split infinitives was invented by nineteenth-century grammarians" did worse: of its first twelve results, only a section of the AMA Manual of Style was on the subject, the rest about invented traditions and nineteenth-century cities. Here, short topic words beat a whole claim.
Citing Fowler's and the MLA page with Cite a source
From the ISBN of Fowler's fourth edition, 9780199661350, Cite a source returned from Open Library, in APA 7:
Fowler, H. W. (2015). Fowler’s dictionary of modern English usage (4th ed.).
Two things need correcting. The record credits H. W. Fowler, who wrote the first edition; this one is edited by Jeremy Butterfield, and the publisher is missing. Corrected: Butterfield, J. (Ed.). (2015). Fowler's dictionary of modern English usage (4th ed.). Oxford University Press.
From the address of the MLA's page it returned:
Is it OK to split an infinitive? (2021, June 2). MLA Style Center. https://style.mla.org/split-infinitives/
The date and title are right, but APA treats the organisation that publishes an unsigned page as its author, so start the entry with Modern Language Association.
With Pro, at $8 a month, Mechanics QA checks a whole paper rule by rule, including the language slips a spell-checker lets through; Verify references, free, checks that every entry on your list is real. Whether to split a given infinitive stays your call and your style guide's.
Quick questions
Is it grammatically wrong to split an infinitive?
No. Merriam-Webster, the American Heritage Dictionary, Chicago, the MLA and Fowler's all accept split infinitives, and English writers have used them since the 1300s.
Who invented the rule against split infinitives?
Nineteenth-century grammarians and letter writers. Merriam-Webster dates the first known edict to John Comly's grammar of 1803; an 1834 letter to the New-England Magazine and Henry Alford's 1864 Plea for the Queen's English objected too.
Does APA 7 allow split infinitives?
APA Style's website gives no rule on them and sends grammar questions it does not cover to a trusted grammar reference, so a split that reads clearly is acceptable unless your course says otherwise.
Is "to boldly go" a split infinitive?
Yes. Star Trek's "to boldly go where no man has gone before" puts boldly between to and go, and Chicago's editors cite it as a split worth keeping.
How do I find out which style guide my assignment follows?
Paste the brief into EdCitation's free Check your paper: it lists the citation style it finds with the sentence it came from. Read the set-aside sentences too, because language rules can be missed.
References
- Alford, H. (1864). A plea for the Queen's English: Stray notes on speaking and spelling (2nd ed.). Strahan. https://archive.org/details/pleaforqueen00alfo
- American Psychological Association. (2024). Grammar. APA Style. https://apastyle.apa.org/style-grammar-guidelines/grammar
- Butterfield, J. (Ed.). (2015). Split infinitive. In Fowler's dictionary of modern English usage (4th ed.). Oxford University Press. https://www.oxfordreference.com/display/10.1093/acref/9780199661350.001.0001/acref-9780199661350-e-5585
- Comly, J. (1823). English grammar, made easy to the teacher and pupil (11th ed.). Kimber and Sharpless. https://archive.org/details/englishgrammarma00coml
- Fowler, H. W. (1926). A dictionary of modern English usage. Oxford University Press. https://archive.org/details/in.ernet.dli.2015.231095
- Goldfarb, N. (2018, April 26). The Economist finally comes around. Language Log. https://languagelog.ldc.upenn.edu/nll/?p=37945
- HarperCollins Publishers. (n.d.). Split infinitive. In The American Heritage dictionary of the English language (5th ed.). Retrieved September 26, 2026, from https://ahdictionary.com/word/search.html?q=split+infinitive
- Inaccuracies of diction. (1834, December). The New-England Magazine, 7, 467–470. https://archive.org/details/sim_new-england-magazine_1834-12_7
- Merriam-Webster. (n.d.-a). Split infinitive. In Merriam-Webster.com dictionary. Retrieved September 26, 2026, from https://www.merriam-webster.com/dictionary/split%20infinitive
- Merriam-Webster. (n.d.-b). To boldly go: Star Trek and the history of the split infinitive. https://www.merriam-webster.com/wordplay/to-boldly-split-infinitives
- Modern Language Association. (2021, June 2). Is it OK to split an infinitive? MLA Style Center. https://style.mla.org/split-infinitives/
- Perales-Escudero, M. D. (2011). To split or to not split: The split infinitive past and present. Journal of English Linguistics, 39(4), 313–334. https://doi.org/10.1177/0075424210380726
- Pullum, G. (2013, September 9). The Economist should lighten up and split some infinitives. Slate. https://slate.com/human-interest/2013/09/split-infinitives-the-economist-magazines-style-guide-says-readers-find-it-annoying-so-never-do-it.html
- Stoyle, G. (2013, June 24). To split or to not split?: The split infinitive past and present. Linguistics Research Digest. https://linguistics-research-digest.blogspot.com/2013/06/to-split-or-to-not-split-split.html
- University of Chicago Press. (n.d.). Split infinitives (Q&A No. 1). The Chicago Manual of Style Online. https://www.chicagomanualofstyle.org/qanda/data/faq/topics/SplitInfinitives/faq0001.html
- University of Duisburg-Essen. (2025). Guidelines for writing assignments and MA theses. Institute of East Asian Studies. https://www.uni-due.de/imperia/md/content/in-east/programs/guidelines_for_writing_assignments_and_ma_theses_2025-05.pdf