Psychologists tried to figure out: Is one space or two after a period better?

Spatial reasoning.
Spatial reasoning.
Image: AP Photo/Elise Amendola
We may earn a commission from links on this page.

In the days of the mechanical typewriter, it was clear what to do when you came to the end of a sentence. But as the number of Americans who grew up on typewriters dwindles, the US elite has been gripped by a divisive dilemma: Between the period at the end of a sentence, and the first word in a new sentence, should there be one space or two? Oh, and how many inches should the margins in Microsoft Word be again?

A study published last week by psychologists at New York’s Skidmore College attempted to answer definitively whether there’s any real difference in how people process text with one space after the final punctuation, versus two. The results showed no major difference in comprehension, but that there were some benefits in readers’ processing of words in texts with two spaces.

Sixty participants were asked to read 20 separate paragraphs, on average about eight sentences long. Each paragraph contained one of four variations: one space after each period and comma; two spaces after each period and comma; one space after a period and two after a comma; and two spaces after a period and one after a comma. Each paragraph was followed by a comprehension question. The researchers tracked participants’ eye movements while they read, as well as their reading times for each paragraph.

The researchers found that the number of spaces had no effect on comprehension or reading speed. (Pedants hoping for a neuropsychological justification for the habits ingrained in them since middle school are out of luck.)

What the study did show were small differences in how people processed what they were reading. Researchers looked at eye movements specifically when participants read areas of text where the periods occurred: the word right before the punctuation, the punctuation, and the word right after. In the previous two sentences, for example, this phrase:

reading. Researchers

The experiment showed that in texts with two spaces after periods, significantly more people skipped this section, and significantly fewer lingered on it, than with texts that had one space after the period. When readers did linger on the area of texts with two spaces after a period, it was for a shorter period of time than they tended to linger on areas of texts with one space after the period. According to the researchers, these are indicators of reader processing—that is, how quickly they identify and grasp the words they’ve just read.

When participants came across commas followed by two spaces, they tended to skip more quickly through the section. Otherwise comma spacing didn’t seem to affect processing, and in fact slowed overall reading speeds (probably because it was such an unconventional way to type a sentence).

One major caveat to this experiment is that the researchers used Courier New, a monospace font often used in programming and eye-tracking studies, wherein each character gets exactly the same width of space. Most fonts you’re likely to come across in everyday reading, online and in print, are proportional fonts, in which the space is allotted to each character is proportional. It’s unclear how this would affect the results of the study.

It seems like the debate over two-spacing, a vestige of typewriting, should be resolved by now. But in 2009, the American Psychological Association caused professorial groans heard round the country when it changed its style guide back to two spaces after the ending punctuation, purportedly because it would make sentences easier to read.