5

In a paragraph of multiple sentences, should there be one or two spaces after each sentence's period for readability?

The paragraph is typed in Arial font. It is size 11 font. The monitor it is being viewed on is Ultra 4k HD. The background is white and the text is black.

I recently read somewhere (with an unknown credibility) that a single space is better, and double space is just legacy style from typewriters. But I was taught to double space, and I personally think double space looks better.

The above text has one space, because that's what the iPhone does.

  • This isn't a great question, it's like asking whether you should use F or C in your design. Honestly I've never learnt to use double space, so I am assuming it's a cultural thing. – insidesin Aug 2 '15 at 19:07
  • Are you sure that you are looking for a double space (that is, two spaces next to each other), and not one of the many other types of spaces? cs.tut.fi/~jkorpela/chars/spaces.html – André Aug 3 '15 at 7:02
  • I wish I could write a full answer but this is one of those things I learned long ago from reading a few articles from authoritative sources. Use one space. I don't remember the reason two spaces were used in the first place, I'm sure Google has the answer for that, but that reason no longer exists so, use one space. – Rob Aug 3 '15 at 10:36
  • re "The above text has one space, because that's what the iPhone does" -- all HTML on all platforms behaves that way, not just the iPhone; if your paragraph is part of a web page, any whitespace will collapse to a single space (unless you force it with  .) – Daniel Beck Sep 29 '16 at 12:24
4

Can open. Worms everywhere.

There is no canonical answer here as its still openly and vigorously debated.

The Wikipedia page on the topic is very well written and has links to research (tl;dr: It's inconclusive).

My own view on this from a UX perspective is:

  • It's a design decision, more than a usage/dogma decision.

  • For digital interfaces (especially browsers) the difference often matters less because UI clients often collapse or reduce the difference between 1 and 2 spaces.

  • If you really care about the spacing even with the caveats above, then as a design matter it will depend on the font size, weight, line spacing, and layout. More spacing after the period provides greater visual separation and more breathing room between the sentences, so the decision depends on whether you want the reader to experience the tiny bit of extra visual and cognitive separation or not.

  • Generally single spacing is considered more "modern" practice, but that is more of a convention than a usability/design decision, because design here is usually overwhelmingly dependent on context.

I'll add some examples later which illustrate these points more clearly.

2

In the same way that having an empty line between chunks of thoughts (i.e. paragraphs) serves as a visual marker which makes reading and scanning easier, a double space after a full stop / period serves as an improved visual marker for the end of a sentence. I can't recall the source, but I read a study a few years ago on just this point which found the result given above.

That said, double spaces after periods have fallen out in larger parts of the world, mostly as a style question. But if you're looking for pure UX without a consideration of your audiences design preferences, I would suggest that a double space is a good idea.

However, it's often fairly moot argument online, as many systems automatically reduce double spaces after a period to a single space anyway.

1

All experts in typography will tell you that one space is correct. For one thing, it eliminates the problem of "rivers," spaces that break apart a paragraph like cracks in the text block.

The universally accepted expert in typography is Robert Bringhurst, and his magnum opus The Elements of Typographical Style has something to say about space after periods on page 28, where he refers to two spaces between sentences as a "quaint Victorian habit" left over from "a dark and inflationary age in typography and type design."

For a more in-depth treatment, see the answer in Butterick's Practical Typography. TL;DR: Always use only one space.

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