To double space or not to double space?

Do you put two spaces after each sentence? Feel free to comment below! I never have– but maybe I should? Read on to find out…


An article recently appeared in the Washington Post with the title “One space between each sentence, they said. Science just proved them wrong.” It was prompted by a recent study, and is promoted (with this click-baitish title) as resolving one of those age-old debates: should there be two spaces, or a single space, in between sentences?

The TL;DR version? The story goes that historically, for legibility purposes, two spaces were always printed in between sentences. Like I’m now doing in this paragraph (although spoiler alert: I don’t normally double space, and don’t think it’s important!). Then along came the computer, creating an explosion of fonts and styles of typography (a topic for another day, but see some of the further reading below!). It was argued that while old fonts, which were all monospaced due to the constraints of the typewriter and printing presses (meaning, each letter had the same width), may have benefited from the double spacing, the new fonts created by computers were not constrained in this way. And it’s certainly true that most of our commonly used fonts nowadays are not monospaced (the most common exception is probably Courier).

People have strong feelings about this issue! Check out a post about it on this other cool blog:
People have strong feelings about this issue! Check out a post about it on this other cool blog:

The new study touted in the Wasingtion Post article (Are two spaces better than one? The effect of spacing following periods and commas during reading) reports that, using eye-tracking methods, it was found that indeed double spacing is better (read more about eye tracking here)! The reporting on this study is a good example of misleading science communication, however– a bit closer look at what the authors actually found, and you’ll see that you shouldn’t start double-spacing if you haven’t been! For those of you who do, the good news is, you may as well keep on doing it.

The best reason to not change your typing habits, based on this study? Probably none of us should ever change our behavior because of the results of one study! This is a basic, but crucial point. If you’ve ever read more than one article on a new finding about what you should or shouldn’t eat or drink, you know this frustration– science works best as compiling results, from different studies, fields, methods, researchers, and labs. So, if all you care about is whether this study has unequivocal evidence to start or stop double-spacing, you can stop reading here: it definitely does not.

So what did they find? This was the first study to directly examine whether single or double spacing is better, and as I mentioned, they used eye-tracking methods, so you can really get a lot of detailed information about how well people were reading. Are you surprised no one studied this before? Well in fact, there are dozens of studies that have looked at spacing, and that used eye-tracking– but they all looked either a t t h e s p a c i n g between letters, or the spacing between words– not just the spacing between sentences.

What did those studies might find, you ask? An amazingly mixed set of results! And what is one of the take-home messages? Two things are really important for determining how spacing will affect you: (1) whether you’re familiar with the spacing (so, you may read worse just because it unusual for you to read that way)!, and (2) which fonts were used in the study.


And sure enough, this new study on double-spacing had results that relate to both of those matters. First, remember that claim that double-spacing was better for monospaced fonts? Well, this study did indeed use a monospaced font (Courier!) and did not test any others. And secondly, and perhaps most crucially, they found a difference between people who normally single-spaced and those who normally double-space. While there was no effect on anyone’s comprehension of the sentences or their overall reading times, people who normally type with double-spacing (which was 21/60 people in their sample), did read more words-per-minute (WPM) when they read sentences with double-spacing, compared to single spacing. For those who normally type with single-spacing, they actually read a little bit fewer WPM in double-spaced paragraphs!

The upshot for the researchers was that they found all participants, whether or not they’re used to double-spacing, basically spent less time looking at the areas of the sentences around the periods, if there were two spaces. But again: this didn’t lead to better comprehension, or even to less time spent reading overall. So while it does seem that, at least for this one study and this one font, everyone may benefit from double-spacing, the benefit is limited to a short-term one: your eyes flow more evenly past the period and onto the next sentence, but this benefit doesn’t add up to anything in the context of the entire paragraph.

So as you can tell, I’m sticking to my single spaces!

Further reading:
The History of Typography – Britannica online

The Evolution of Typography

Is it true that we don’t look at every word when we’re reading? What are our eyes doing when we read?

Aoccdrnig to a rscheearch at Cmabrigde Uinervtisy, it deosn’t mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a toatl mses and you can sitll raed it wouthit porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.”


You’ve probably encountered that paragraph before (or, if you’re like me, a bunch of times—it seems to go viral every other year!). How true is this claim that “the human mind does not read every letter by itself, but the word as a whole”? The first part has some truth to it—we do not focus on each letter in a word as we read—but the second part is very misleading! It is a pernicious myth that we learn to read by memorizing words as a whole shape. And it’s easy enough to come up with examples where jumbling letters in this way is a real problem—calm becomes clam, blow becomes bowl, etc. So, what do we actually need to look at, when we’re reading?


As you’re reading this sentence, you might feel that your eyes are moving smoothly across it. In fact, when we read text, whether its on a printed page or a computer screen, our eyes more in a series of short jumps, called saccades. These saccades are very fast, around 20-35 milliseconds, and in between them our eyes fixate on the text. These fixations can be brief (150 milliseconds), or relatively long, say one half of one second.


So, what is it that we look at during these periods of fixation? It is true that we do not focus on every single word when we’re reading—this is more or less for two reasons. First, we’re able to perceive several letters within the fovea (the center of our gaze): in languages like English, which are written from left to right, we can see a few letters to the left of our fixation and maybe 12-15 to the right (in languages written from right to left, like Arabic and Hebrew, readers can perceive more letters toward the left of fixation that the right!). This means that during each fixation, we take in a few words at a time, unless there are very long words. When we saccade to our next fixation, we are able to skip over some words because we actually have already seen them. This means, of course, that one of the challenges of reading is remembering the words and letters you have recently seen (in working memory) and integrating them with new information, as you continue to saccade through the sentence.


The second reason we do not need to fixate on every word is because we are often able to predict what words are going to follow—and we can use this ability to predict to speed our reading. This is often true of function words (words like “to”, “the”, and “do”), but also in sentences where the context leads to a very high probability for a certain word. Imagine that in one fixation you read “They sang Happy…”—you can guess that almost definitely the next word is “Birthday” (in fact, when we read sentences where we expect one word and it ends up being another, this surprise has consequences—it will cause us to slow down dramatically in our reading speed and often to double back and re-read!).


How do we know these things about reading? Mostly through the use of a machine called an eye tracker, which allows us to know (with very high temporal precision) where someone is looking. There are many videos online where you can see demonstrations of an eye tracker at work. This one in particular “How we read shown through eye tracking”) shows how we move our eyes from one line of text to the next—and how this is affected by the way that the lines are (or are not) justified!



“Eye movements in skilled readers”

“What eye movements during reading reveal about processing speed”

“How we read shown through eye tracking”