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Some things about typesetting "et al." seem obvious: make sure the period is followed by \ unless it's also the end of the sentence, use ~ before if you don't want it to end up alone in a new line.

What about the space in the middle, though? Reasonable options seem to include:

et al.
et~al.
et\hspace{.16667em}al.
et\,al.

I could not find any style guide or recommendation online.

Which variant is advisable? Are there citable references about this?

Rationale for half space: while et and al. are technically two words, they form an abbreviation together. Hence, I think the rules of compound abbreviations (e.g. e.\,g.\) apply.
Also, "al." alone at the start of a line looks weird. And lonely.

Raphael
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  • biblatex's english.lbx uses et\addabbrvspace al\adddot where \addabbrvspace is a "normal" space penalized by a special abbreviation penalty. (biblatex.def has The counter 'abbrvpenalty' holds the penalty used in short or abbreviated bibliography strings. For example, a linebreak in expressions such as "et al." or "ed. by" is unfortunate, but should still be possible to prevent overfull boxes. We use TeX's \hyphenpenalty [...] as the default value. The idea is making TeX treat the whole expression as if it were a single, hyphenatable word as far as line-breaking is concerned.) – moewe Oct 12 '15 at 10:00
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    At first I thought I might prefer et\,al. but after seeing the result it find it does look a bit cramped so I would go with et~al.. With e.\,g. the thin space looks better because the . provides some visual spacing. – moewe Oct 12 '15 at 10:06
  • I'm actually more interested in breaking vs non-breaking; I figure that the length of the space if a matter of taste. The context is this discussion about what CSL styles do. HTML resp. browsers have limited facilities, so I guess it's breaking or not. (What Biblatex does seems smart.) – Raphael Oct 12 '15 at 10:09
  • Mhhh, maybe this more one for Graphicdesign or the language SXs then. I would try to avoid a line break if possible, but if a break is really necessary I would be OK with one there. Apparently DIN5008 wants a full-length protected space in abbreviations like z.\,B., but I'm not sure what they say about et al.. One could argue that the "et" isn't even abbreviated. – moewe Oct 12 '15 at 10:18
  • @moewe DIN5008 does not seem to distinguish full and half spaces at all (what a disappointment). They also write "Leerzeichen" as divider in numbers, which ... no. – Raphael Oct 12 '15 at 13:25
  • Well, yes, but I thought you were not concerned with thin vs. full-width spaces? DIN/ISO norms are not my favourite sources for style questions (have you seen their bibliography style?), but at least they are an "authoritative source" in one way or another. (Which is what you seem to need to win your argument.) See also Canonical way to typeset spacing in abbreviations, Good practice on spacing. – moewe Oct 12 '15 at 14:22
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    The word "et" is not an abbreviation and should not be subjected to a thinspace requirement. If you want to work on the analogy of e.\,g., then I'd expect you to be using e.\,a., which few would be able to recognize. However, it is fine to discourage the break, as biblatex does. – jon Oct 12 '15 at 16:53

1 Answers1

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I think the most elegant solution in the context of TeX would be to discourage a line break inside et al. but without ruling it out altogether. This suggests to define a macro as there is no equivalent of ~ for this.

\documentclass{article}

\def\etal.{et\penalty50\ al.}

\begin{document}

Lorem \etal. ipsum \etal. dolor \etal. sit \etal. amet, \etal. consetetur
\etal.  sadipscing \etal. elitr, \etal. sed \etal. diam \etal. nonumy
\etal. eirmod \etal. tempor \etal. invidunt \etal. ut \etal. labore \etal.
et \etal. dolore \etal. magna \etal. aliquyam \etal. erat, \etal. sed
\etal. diam \etal. voluptua.  \etal. At \etal. vero \etal. eos \etal. et
\etal. accusam \etal. et \etal. justo \etal. duo \etal. dolores \etal. et
\etal. ea \etal. rebum. \etal. Stet \etal.  clita \etal. kasd \etal.
gubergren, \etal. no \etal. sea \etal. takimata \etal.  sanctus \etal. 

\end{document}

enter image description here

Note that the dot in \etal. is part of the definition. This makes it easier to deal with space following the macro. I could not have used \newcommand for this. I have used a full space (\) inside but something like \thinspace or \, would also work, of course.

That being said, I think it is perfectly fine to not treat et al. special in any way and to care about more jarring typographical problems first (like ALL-CAPS acronyms).

Christian Lindig
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    This is actually exactly what biblatex does with et\addabbrvspace al\adddot (as explained in my comment above) and definitely a very good solution. – moewe Oct 12 '15 at 14:23
  • Could you show the definitions of the two macros? – Christian Lindig Oct 12 '15 at 16:12
  • You can find them in biblatex2.sty. For \addabbrvspace it is \newrobustcmd*{\addabbrvspace}{\unspace\blx@postpunct\penalty\value{abbrvpenalty}\space\blx@imc@resetpunctfont} (modulo %s and line breaks) where \defcounter{abbrvpenalty}{\hyphenpenalty} is defined in biblatex.def the explanatory text I quoted in the comment can be found there as well. (The definition of \adddot is a bit more convoluted and not relevant here.) – moewe Oct 12 '15 at 16:22
  • Interesting. The definition of ~ in plain.tex is simpler: \def~{\penalty10000\ } where in plain.tex 10000 is written as \@M. The penalty for a hyphen is 50, by the way. – Christian Lindig Oct 13 '15 at 07:29
  • Well, \addabbrvspace does more than just inserting the space, it also clears any space that might have been added before it and does some stuff with fonts. The value of \hyphenpenalty is also mentioned in the text in biblatex.def, I omitted that when quoting it above though. – moewe Oct 13 '15 at 08:03
  • @moewe What is the latex package for \addabbrvspace ? – Cyriac Antony Feb 01 '21 at 05:01
  • @CyriacAntony The version I was talking about is defined by biblatex (I don't know if there are other packages that define a command of the same name or if there are packages that define a similar command with a different name). – moewe Feb 01 '21 at 06:26