LaTeX pet peeves

🕑 12 min • 👤 Thomas Graf • 📆 July 07, 2020 in Tutorials • 🏷 student advice, LaTeX

Somehow I wound up with five students writing their theses this Spring semester, and you know what this means: lots and lots of reading. And when reading, I can’t help but get riled up every time I see one of my LaTeX pet peeves. I also like to read the source files in parallel with the PDF, and over the years I’ve come across some nightmare-fuel coding in those files.

So, in a (futile?) attempt to save my future self’s sanity, here’s a list of all my LaTeX pet peeves. Many of them are covered in your average LaTeX tutorial, but people rarely read those cover to cover and instead just go to specific parts that they need to solve whatever problem they’re wrestling with. Compiling it all into a single list might make for a more useful reference. Future students of mine, read this and adhere to it. You have been warned!

Using LaTeX where it isn’t needed

Alright, let’s start with the most important one: only use LaTeX if it’s the best tool for the job. LaTeX is the unrivaled champion when you have to do a lot of heavy lifting: bibliographies, references, multi-part documents, math, trees, autosegmental tiers, automata, glossed examples, data plotting, a single document for producing both handouts and slides; LaTeX handles all of that, um, perhaps not well, but better than any other solution on the market. Beware, though: with great power comes great responsibility, and a lot of my pet peeves are actually examples of the writer not paying attention to the subtle details of LaTeX that are the source of its power.

Great power also means a certain degree of clunkyness. For simple jobs, simpler tools are more efficient. If all you have to show me is a todo list, write that in a markdown dialect and convert it to PDF with pandoc. If it’s powerful enough for an outdex post, it’s probably powerful enough for whatever collection of notes you want to show me in our meeting.

Not using labels and references

If I see a hardcoded reference like Section 1 in the source code, my blood pressure spikes. The whole point of LaTeX is that you don’t have to do these things. Liberally assign labels, and then use them, e.g. Section~\ref{sec:some_section}.

Be systematic with your labels. For instance, I like the format \label{type:container_name}, where type could be

  • cha for chapters,
  • sec for sections,
  • ssec for subsections,
  • fig for figure,
  • tab for table,
  • ex for example.

And container is the name of the containing unit. If a thesis contains a subsection in a chapter with label \label{cha:foo}, then the subsection would get the label \label{ssec:foo_bar}. That system isn’t perfect as it creates quite a hassle when I decide to make a subsection its own section, but it provides a rudimentary typing system for the document.

And if you reference a section that doesn’t exist and/or doesn’t have a label yet, don’t just omit the reference. Use \ref{type:container_name} based on what the label should be. That way, you won’t forget to insert the reference later on, and when you finally get around to writing that section, you already have a record of which other sections tie into it.

Oh, and because I’ve seen this mistake an estimated 328 times by now: labels in a float (figures, tables) must be specified after \caption, not before.

Not using macros

The whole point of LaTex is to separate content from presentation. Don’t write something like $\text{the} :: =\mathrm{N} \mathrm{D} -\mathrm{nom}$. It’s tedious, prone to errors, and lacks semantics. Just define a bunch of custom macros:

With those macros, you can rewrite the code above as \mlex{the}{\fsel{N} \fcat{D} \flce{nom}}. That’s easier to read, and it conveys clearly that you’re defining a lexical item with selector feature N, category feature D, and licensee feature nom. And if you decide later on that you want to use a different notation for features, you only have to change the macros.

Subscripts

One quirk of LaTeX is that it only provides subscripts in math mode. So a writer that desires, say, labeled bracketing with subscripts, might try the following code:

This is wrong, wrong, wrong. In math mode, LaTeX treats each character as a separate mathematical variable and inserts some white space between them. So $_{VP}$ is actually interpreted as $_{V P}$. Instead of a single subscript VP, you get two subscripts V and P.

The difference is pretty blatant once you’re aware of it. Here’s the output produced from the code above.

The subscript letters are too far apart
The subscript letters are too far apart

And here’s what it should look like:

Correct subscript spacing
Correct subscript spacing

Notice the decreased spacing between V and P.

The second output is produced by replacing $_{VP}$ with $_\mathit{VP}$:

This now typesets VP as a single variable in math italics.

Alternatively, you could also use $_\text{VP}$ or $_\textrm{VP}$ to have the label typeset as normal text.

Subscript typeset with \textrm
Subscript typeset with \textrm

Quite generally, may I suggest you define a custom macro for the subscripts of labeled brackets?

This way, you can change the definition of the macro to fit the layout of your paper. This separation of code and output is exactly what makes LaTeX so powerful, so make generous use of it! In fact, why don’t you just use the following macro for your labeled bracketing:

This macro allows you to produce the output above from \labbrack{CP}{John \labbrack{VP}{arrived $t$}}.

Ensure math with, well, \ensuremath

Some of the macros above use a command you might not have seen before: \ensuremath. The name tells you exactly what it does: it ensures that its argument is typeset in math mode. When you need math mode inside a macro, you should always use \ensuremath.

Crucially, don’t try to do something like the following:

This is a disaster waiting to happen. If you use this command while you’re in already in math mode, then the first $ will switch you back into text mode and LaTeX will complain that you can’t use _ in text mode. This doesn’t happen with \ensuremath: if you’re not in math mode, it switches you into math mode, and if you’re already in math mode, it keeps you in math mode.

gb4e’s automath

Some of you might say that we don’t need any of that subscript hackery because the package gb4e redefines _ so that it can be used in text mode. This is a bad solution as it tends to break packages in weird ways that are difficult to debug. Just spare yourself the hassle and turn that “feature” off:

And while you’re at it, you might also want to add a bit more boilerplate around gb4e to make sure it doesn’t throw some odd error messages on recent TeX distros.

Yes, gb4e is pretty broken nowadays. But it’s still better than linguex in that it actually respects LaTeX’s split between commands and environments and doesn’t encourage bad coding choices (context-sensitive commands like \Next and \Last undermine the strengths of the LaTeX labeling mechanism). Here’s hoping somebody comes up with a completely new package, based on tikz matrices — what are you looking at me for?

Punctuation

Alright, this one is really a major flaw in LaTeX’s design, so I don’t blame anybody who gets this wrong. LaTeX makes a distinction between a sentence-ending dot and other uses of dots, in particular as part of an abbreviation. The former has more whitespace after it to create a visual separation between sentences. So far so good, that’s a nice feature.

The problem is that LaTeX, in a misguided attempt to simplify the writer’s life, automatically switches between those two types of dots. By default, dots after lowercase characters are taken to be sentence-ending, and dots after uppercase characters are not taken to be sentence-ending. This is a major pain in the butt. Consider the following example.

The space after CP is too narrow, the one after e.g. is too wide.
The space after CP is too narrow, the one after e.g. is too wide.

LaTeX’s punctuation rules do exactly the wrong thing here. The dot after CP will be interpreted as part of an abbreviation when it is in fact sentence-ending. And the dot after e.g. will be interpreted as sentence-ending when it is in fact part of an abbreviation.

In order to fix this, we have to hack the code to override LaTeX’s default choices. We can put \@ in front of a dot that we always want to be sentence-ending, and we can put a backslash before the space right after an abbreviation.

Correct spacing for sentence-ending dot and abbreviation dot
Correct spacing for sentence-ending dot and abbreviation dot

So LaTeX forces you to not only keep in mind what kind of dot you want, but to also track the context of the dot to determine if it needs special diacritics to get what you want. This is crappy design, but at least you’ll quickly develop the required muscle memory to work around this crappy design.

~ is your friend

There is actually a third solution for the spacing issue pointed out above. Instead of adding a backslash before the space, we could have replaced the space with a tilde.

Tilde can be used instead of backslash to avoid linebreaks
Tilde can be used instead of backslash to avoid linebreaks

This also produces a normal-width space, but it also tells LaTeX that it shouldn’t put a linebreak right after the abbreviation. Either e.g. a stays on the current line, or it all goes onto the next line, LaTeX can’t keep e.g. on the current line and put a on the next. Abbreviations at the end of a line look rather odd, so I generally put ~ after every abbreviation I use. It’s pretty much become muscle memory by now, and I just don’t use the backslash after abbreviation dots anymore.

You can go with whichever one of the two you prefer. But you should use one of them. Don’t just write e.g. a, the spacing will be wrong. It’s a very minor thing, but again, once you’re aware of it you’ll be annoyed when you see a paper that get’s this wrong.

Ellipsis

Since we’re already on the subject of punctuation, ... is not how you typeset an ellipsis in LaTeX. The command for that is \ldots, and again the difference is in the spacing. Just compare:

Ellipsis at end of a sentence
Ellipsis at end of a sentence
Ellipsis in the middle of a sentence
Ellipsis in the middle of a sentence

Quotation marks

My next pet peeve is actually covered early on in every LaTeX tutorial, yet I still get papers that consistently do it wrong: don’t use " for quotation marks. You want \`for opening quotation marks and’’` (that’s two single quotes) for closing quotation marks. Again the difference in typesetting is immediately apparent:

Quotation marks must not be " in the source code
Quotation marks must not be " in the source code

Yes, this is just ridiculous and could easily be handled automatically (many LaTeX editors will do it for you), but LaTeX gonna LaTeX.

/ and \slash are not the same slash

Another bit of LaTeX voodoo. While / does indeed produce a slash, sometimes it’s recommended that you use \slash instead. The difference is that / is a non-breaking character, which means that LaTeX isn’t allowed to insert a linebreak before or after it. Sometimes that’s a good thing. You really don’t want the CG type S/NP to be split across two lines. But with, say, consonantal/non-vocalic, you’ll probably get weird spacing if LaTeX isn’t allowed to break this up into consonantal/ and non-vocalic. So even though their output looks the same, / and \slash don’t do the same thing.

Personally, I think it would’ve been better to have a compositional system where we can use a special marker like | to indicate that the preceding symbol is a non-breaking character. Then ~ would just be a shorthand for a space followed by |. Oh well, the LaTeX code base is 40 years old by now, it’s bound to have its quirks.

\epsilon isn’t the epsilon you want

You thought we were done with LaTeX curiosities, hmm?

This one is not the mistake I see most often, but that’s just because not every student paper has a need for the epsilon symbol. But when a paper does use epsilon, there’s a good chance it won’t be the symbol that the student had in mind. For some reason, most LaTeX fonts use a shape for epsilon that doesn’t look like the typical epsilon. They produce \(\epsilon\) instead of \(\varepsilon\). If you want \(\varepsilon\) instead, you have to use \varepsilon rather than \epsilon.

…and < and > aren’t tuple brackets

Again this one doesn’t show up that often simply because not every paper needs to typeset tuples, but when it’s necessary, people get it wrong oh so often. And in this case, it’s not even LaTeX being needlessly obtuse. Tuple brackets are not the same as \(<\) and \(>\), they have very different angles: \(\langle\) and \(\rangle\). If you want the latter, you have to use \langle and \rangle (left and right angle).

Tuple brackets also have completely different spacing:

  • Using < and >: \(<a, b>\)
  • Using \langle and \rangle: \(\langle a, b \rangle\)
Tuple brackets are \langle and \rangle, not < and >
Tuple brackets are \langle and \rangle, not < and >

Again I’d suggest using a custom macro to make your life a little easier.

You could also use a version with automatic sizing of the tuple brackets, but this will often give you problems if LaTeX needs to insert a linebreak.

Math relations and operators

The spacing difference between < and > on the one hand and \langle and \rangle on the other is actually an instance of a more general principle. In math mode, LaTeX distinguishes between normal symbols, operators, and relations, and they each have different spacing properties. So instead of a R b, you should write a \mathrel{R} b to get the correct spacing. If you want | to be an operator, you should write a \mathop{|} b. Again it’s a good idea to use custom macros for that.

Math relations and operators have different spacing
Math relations and operators have different spacing

So, many, dashes

Another subtle difference, this time with respect to hyphens and dashens.

  • - is a hyphen and is used word-internally, e.g. in single-dashed
  • -- denotes a range, e.g. pages 55--68 (yes, this means you should use -- for page ranges in bibtex entries)
  • --- is an em-dash and is used with parentheticals, e.g. John---as far as I'm aware---snores
  • $-$ is a minus and should only be used in equations: \(15 - 3\)
LaTeX has various kinds of dashes
LaTeX has various kinds of dashes

I like to even add spaces around the super-wide ---, and every single copy editor tried to dissuade me from that. I like the extra space, but I’m sure it’s somebody’s pet peeve, so, sorry about that.

Bibtex capitalization

As you might know, your bibtex style automatically handles the capitalization of your references. But it only works well if

  1. your bibtex references are in Sentence Case, and
  2. you explicitly indicate which characters should not be lowercased.

So don’t write something like this:

There is no easy way to convert this to Sentence Case if that’s what the publisher wants. And if the publisher want’s lowercase, you’ll get mgs instead of MGs.

Instead, it should be:

This way, you will get the correct lowercase or sentence case depending on the publisher’s stylesheet, and either way MGs will stay MGs and won’t be lowercased to mgs.

More to come

Okay, this is already a laundry list of things that are easy to miss when writing but leap out at the reader that’s aware of them. But we’re not done yet, I have another list that’s all about doing figures with TikZ. In comparison to LaTeX, TikZ feels a lot more like an actual programming language, so there’s a much higher risk to write working but really nasty code. Getting proficient with TikZ is hard, the manual is over a 1000 pages by now. But I think there’s some general design principles that even newbies can follow easily and that make TikZ code a lot more fun to work with. So the next time we return to LaTeX (and I’m not saying that’s anytime soon), be prepared for some unsolicited TikZ advice by yours truly.

In the meantime, feel free to share your personal LaTeX pet peeves in the comments section. There’s so many subtle issues, I’m sure there’s some common mistakes that I still make myself.