The Legibility of Serif and Sans Serif Typefaces (2022)

That's the default state of all questions. It doesn't need to be explained.

Why do you think people had opinions on whether Pluto should be called a "planet"?

As for where it came from to me it very much feels like the defense of serif typefaces is largely typographers defending existence of their craft and people talking past each other with overgeneralized claims. There is definitely value in the art and craft of typography and I respect that. It would be too bland if everything used plain sans serif fonts that barely differ from each other, and you can definitely mess up typography making text hard to read when done badly. But I also believe that there is plenty of things based on traditions and "everyone knows x because that's how we have always done it".

As for sans serif for screens the obvious reason and also thing that comes up multiple times is low resolution text. At certain resolution there are simply not enough pixels for serifs. The author of paper suggest that with modern high resolution screens this argument doesn't stand. My personal opinion is that it's not a big issue at sufficiently high text size. But even on somewhat modern 2560x1440 screen I can find plenty of UI elements that have only 7-8 pixels high labels. Not everyone is using retina displays and not everything is long format text. Screen resolutions have increased, but so have information density compared to early computer screens, although there is recent trend of simplifying UI to the point of dumbing it down and adding excessive padding all over the place. There are other screens beside computers and mobile phones, many of them not very high resolution even by standards of early computer screens. It doesn't make sense to put high resolution screen and Linux computer in every little thing. Problem is made worse by lack of antialised text sometimes due to screen, sometimes MCU memory and compute limitations. You are probably not going to have modern font rendering stack on something like black and white washing machine screen, gas station pump or thermostat The research multiple times mentioned stuff like low resolution, but it hardly ever quoted hard numbers in a meaningful way. How many pixels a typeface needs to be comfortably represent serif? How many arcseconds? Surely there must be research related to that one. This might be part of problem for some comparative research - can't compare readability of serif/sans serif if there is no serif typeface at those resolution. Stuff like point 10 or point 12 without additional details is meaningless.

Some personal anecdote -> text antialising has huge effect. Made a sample text of serif and sans serif font and zoomed out to the point where lower case letters are ~6px high. I wouldn't expect there to be enough resolution for serif but you can perceive surprising amount of detail in letter shapes. Zoomed in on screenshot it's a blurry mess, but at normal zoom level the serif letters are fine. It's readable but wouldn't consider either of 2 comfortable. When scaled up to 8px both pieces were still harder to read than same height text in UI labels. Why is that? Why is one identical height sans serif text much more readable than other? Are UI labels better pixel aligned? Is it due to subpixel antialising? That's on a 90deg rotated screen, is subpixel antialising even working properly there?

Just for fun switch OS UI font to serif. Due to font sizing inconsistency it ended up being 1 pixel shorter (7px) than same size default UI font. Can those even be considered serifs when they are hardly a pixel each? It felt weird, nowhere near as bad I expected, but still weird.

- serif was claimed to lead to better horizontal tracking... so better for long prose readability

- sans serif was claimed to lead to better spot-recognition of characters... so better for spot-character/word recognition and legibility

Those effects were never very strong, and varied depending on the exact fonts in use (and for digital, font rendering characteristics).

There's also probably an effect based on what you're used to. If most of the books you read are serif (which they would be for older people, since almost all printed books were serif), and your exposure to sans serif was largely via the internet, and you don't like most of what's written on the internet, that might sway you toward serif. Conversely, if you mostly read modern internet text, you might have the opposite bias.

I'm not sure if my browser is broken or what but they literally look identical to me in your comment.

Hacker news uses sans-serif font and in all my browsers the I and l look nearly identical btw.

So a form might have a choices between ASCII, Hex, Base52, Base64, or schemes with anti-typo check digits, etc.

The sans-serifs designed before WWII have evolved towards a maximum simplification of the letter forms, eliminating not only the serifs, but also the contrast between thin lines and thick lines and also some other details of the shapes that differentiate the letters. The extreme simplification was achieved in some of the "geometric" sans-serifs, where most of the letter shapes were simplified into circles and straight lines. The motivation for shape simplification was that in the beginning the sans serifs were intended for advertising, i.e. for printing on cheap paper with cheap devices, which could not reproduce fine details. More over such texts were intended to be readable from great distances, from where fine details cannot be perceived.

After WWII, some sans-serifs have just reproduced with negligible changes some of the earlier sans-serifs, e.g. Helvetica and the like.

Most of these sans-serifs, like Arial, are extremely bad for use in computers, because they have a lot of ambiguous letters and digits. That mattered less for English texts, which have high redundancy, allowing the guessing of the intended letters, but in computers there are a lot of abbreviations, keywords, identifiers, expressions and other kinds of character strings with low redundancy, where it may be difficult or impossible to recognize the intended letters or digits.

However, there are also several kinds of very different sans-serifs among those designed after WWII, which attempt to remove the disadvantages of the classic sans-serifs.

One kind is the sans-serifs that have only the goal to remove all ambiguities in letters, digits and other symbols, like most of the monospace typefaces intended for programming.

Another kind, besides removing ambiguity also reintroduces some of the letter shapes from serifs, which have been simplified in the classic sans-serifs, e.g. double-storey "g" and "a", old-style digits, distinct shapes for the italic variant of a font, etc. These slightly more complex shapes increase the distinctness of the letters and digits, making them more easily recognizable. An example of such a typeface is FF Meta.

Finally, there is another kind of sans-serifs that also reintroduces the contrast between thin lines and thick lines. Moreover, among these there are typefaces, e.g. Optima or Palatino Sans, which (on displays with high enough resolution) produce an optical effect similar to serifs, which is achieved not with serifs but by replacing the straight side edges of the lines with slightly concave edges.

In my opinion these kinds of sans-serifs that are intermediate between classic serifs and classic sans-serifs are superior to both classic types, especially for computer use.

Despite being less affected by low screen resolutions, the classic sans-serifs like Helvetica, Arial and many others should never be used for anything, because of their ambiguous glyph shapes.

Serifs have non-ambiguous glyph shapes, but they are heavily distorted at low-screen resolutions or when seen from a distance, so they are also not recommended in many applications.

The good choice is in most cases to use one of the sans-serifs with non-ambiguous glyphs, or for a more beautiful text one of the typefaces inspired by FF Meta or one of those inspired by Optima. For example, my default typeface is Palatino Sans.

Any study about the legibility of serif and sans-serif typefaces that does not include a separate category for non-classic sans serifs is deeply flawed and its results are meaningless.