Q. Please explain your recommendation for using one space after a period in light of this article: James Hamblin, “The Scientific Case for Two Spaces after a Period,” The Atlantic, May 11, 2018.
A. As The Atlantic article reports, a small study conducted at Skidmore College found that spacing between sentences does influence how people read and that some people read faster if there are two spaces rather than one. But the results weren’t definitive, as the study’s conclusion admits:
Punctuation spacing had no effect on the likelihood of regressing back to the punctuation region after leaving it, did not affect comprehension, and only increased overall reading speed for participants who already type according to this two-space convention (who only showed a 3% increase in overall reading speed). Thus, while period spacing does influence our processing of text, we should probably be arguing passionately about things that are more important.
See Rebecca L. Johnson, Becky Bui, and Lindsay L. Schmitt, “Are Two Spaces Better than One? The Effect of Spacing following Periods and Commas during Reading,” Attention, Perception, & Psychophysics 80 (2018): 1510. We agree with that conclusion—except maybe for the part that discourages passionate arguing about small things. For another look at this issue, including some historical background, see “One Space or Two?,” at CMOS Shop Talk.
[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]
Q. I saw someone sharing a post recently stating that you now support two spaces after a period, falling in line with AP style. Is this correct?
A. Don’t believe everything you read. Neither Chicago nor AP nor any other style that we know of—including APA, as of the seventh edition of its style manual, published in late 2019—recommends more than one space after a period. See our post on this subject and its long history at CMOS Shop Talk.
[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]
Q. When did CMOS first recommend one space (instead of two) after periods and colons? I found the one-space rule in the 15th edition, but I remember hearing somewhere that it goes back to the 13th edition. I’m trying to win arguments with people who claim it’s a “new” rule.
A. The sample typewritten manuscript page in CMOS 13 (1982) shows two spaces after a period; in CMOS 14 (1993), it shows one (fig. 2.1 in both editions). But CMOS 15 (2003) was the first edition to make an explicit recommendation for one space after a period (or a colon) in typed manuscripts. It’s a little more complicated for published documents. The 1st edition (1906) described a system of variable spacing that was the norm at the time. (For example, an “em quad” was recommended between sentences—three times the amount of space required between words.) By 1949, when the 11th edition was published, equal spacing was the rule: “The standard for composition [typesetting] such as that in the text of this book would be a 3-to-em space [a third of an em] . . . between words, after colons, after exclamation and interrogation points, and after periods ending sentences” (11th ed., p. 8). So “one space” is a relatively new convention for manuscripts but less new for published documents.
[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]
Q. I recognize all writing formats today say there is to be one space between the period of a sentence and the first letter of the next sentence. I believe this fails to take into account studies that refer to visual cues that assist the reading process. So I start here with you to request this be fully discussed and reviewed with the hope that we may at minimum note that two spaces are acceptable between sentences. Thank you for your consideration of this matter.
A. I’m so sorry to report that that ship sailed long ago. You are a lone voice, crying in the wilderness. Too little, too late; a bolted horse, a dollar short. No metaphor can express how hopeless this is. Our best advice to you is to look for a silver lining in the single space.
[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]
Q. I took typing in 1967 and was taught the two-space convention and have used it ever since. That is, until one of those pesky millennials complained and slapped me with your website. When did the convention change?
A. I’m afraid we can’t pin this one on millennials! The convention changed quite a while ago. (Our Q&A has covered the topic more than once, and you can read more about it at Wikipedia.)
[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]
Q. All right then! I’m steadfastly attempting to adopt the “one space after concluding punctuation” rule. It’s not an easy task for a retired English teacher in his late sixties—one who preached the old rule to legions of eager-eyed scholars. Are there any retraining suggestions that assist the elder learner? I’m tired of correcting my continual errors. I am diligently trying, though.
A. Good for you! The easiest way might be for you to leave the mistakes in place until the document is finished, then use the Find and Replace feature to eliminate all double spaces. In the Find box, type two spaces, and in the Replace With box, type one space. Hit Replace All—and you’re done. (And eventually, when your word processor regularly tells you that the search item was not found, celebrate!)
[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]
Q. About two spaces after a period. As a US Marine, I know that what’s right is right and you are wrong.
I declare it once and for all aesthetically more appealing to have two spaces after a period. If you refuse to alter your
bullheadedness, I will petition the commandant to allow me to take one Marine detail to conquer your organization and impose
my rule. Thou shalt place two spaces after a period. Period. Semper Fidelis.
A. As a US Marine, you’re probably an expert at something, but I’m afraid it’s
not this. Status quo.
[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]
Q. Help. How many spaces do you leave after a colon in a manuscript?
A. One space after a colon. There is a traditional American typing practice, favored by some, of leaving two spaces after colons and periods. This practice is discouraged by the University of Chicago Press, especially for formally published works and the manuscripts from which they are published.
[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]
Q. Please help. I have confusion regarding the correct spacing after periods and other closing punctuation. My company uses the font Arial and consistently uses a flush-left margin. We are an engineering company. My job consists in preparing documents and letters for customers. Everything I read in manuals and from technical writers directs me to use one space after periods. I find that it works very well, except occasionally, when an extra space helps readability. Knowledgeable engineers have embraced the one space use as being consistent with the font design and automation of reports. Others are unpleased with the one space, they think they have difficulty reading. (I, too, had an adjustment period which I forced myself to endure until it became automatic to read easily.) We are preparing technical information. What do you think? Thanks for your wonderful support and especially the quick answers. I greatly appreciate your service.
A. Published work these days rarely features two spaces after a period. In the era when type was set by hand, it was common to use extra space (sometimes quite a bit of it) after periods, a practice that continued into the first half of the twentieth century. And many people were taught to use that extra space in typing class. But introducing two spaces after a sentence-ending period—and only after those periods—causes problems. Absolute consistency is easy to monitor when double spaces are never allowed, but less easy when some spaces after periods are double and others single (such as those at the ends of abbreviations and initialisms in running text). Since there is no proof that an extra space actually improves readability—as your comment suggests, it’s probably just a matter of familiarity—CMOS follows the industry standard of one space after a period.
[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]