For the first “real” episode in this series, I wanted to start very slowly. Let us take a look at very basic typographic symbols, namely dots and dashes (and some spaces). Except for the rules about hyphens, dashes, and the like, all the rules presented here are more about aesthetics and custom.

Dots

We use a simple full stop (or period for you Americans) to indicate the end of a sentence. Nothing new here so far.

When we want to indicate a multiplication in a formula, sometimes it makes sense to show a multiplication symbol. In this case, the proper symbol to use is \cdot (for LaTeX users) or · (for HTML). This symbols is typeset as · and it is also used to indicate a transition between words, for example on a business card. A sample business card might read “John Doe · Tinker & Tailor”.

Never, never use \times or × to indicate multiplication in any mathematics text written for university students. In the classroom, you might find “5 × 4 = 20”, but the × symbol is customarily used to indicate things like a cross product in mathematics.

If you want to indicate that something is missing from a quotation, a typeset matrix, or anything else, use the wonderful ellipsis character. It consists of three dots that are spaced differently than three regular dots. In LaTeX, you can use \dots. In HTML, use …. It looks like this:

1,2,3,…,n

The advantage of the predefined ellipsis character is that it will not be broken up. Some style guides ask you to write an ellipsis as a sequence of dots and spaces. They are wrong. There is a difference between “. . .” and “…” in all fonts.

Dashes

Now let us dash to the dashes! There are three types of dashes. First, we have the simple hyphen, which is technically not a dash but I am calling it one anyway because one usually thinks of it as a dash. Second, we have the en-dash. Third, we have the em-dash.

The hyphen is typeset using a simple - character. We use it to indicate a break in a word, when said word needs to be split because the end of a line has been reached. We also use it to spell some composite words, such as good-hearted or mother-in-law. A further use of the hyphen is to remove ambiguities in some compound adjectives. For example, small-arms fire, high-school students, and so on. XKCD 37 also has a nice example for this.

I do not know all the rules about when to use a hyphen or not. As a non-native speaker, I am slightly biased here. When in doubt, consult your dictionary of choice. At least you now know what the hyphen is meant for.

Moving on to the next dash, the en-dash. In LaTeX we set it by typing two dashes (--). In HTML, we write – to obtain “–”. The en-dash is customarily used to indicate ranges. For example:

The theorem is proved on pages 23–42.

1887–1895 was the period of the first construction of the Kiel Canal.

Most bibliographical services in the web are unable to get the en-dash right. I am looking at you, ACM and IEEE.

The en-dash is also used to indicate joint authorship, such as the Barnes–Hut simulation.

Last, the em-dash. It is the longest of all the dashes. In LaTeX, it is typeset by three hyphens in a row ---. In HTML, use the entity —. The em-dash is rather long, “—”. It is used to indicate a break between parts of a sentence. Most typographers consider it stronger than a comma but weaker than a semicolon or a pair of parentheses. If this comparison does make sense to you, please use the em-dash. Here is an example from my own writing:

Topologists aim to identify invariants of such spaces—properties that do not change when the space is stretched, bent, and twisted by homeomorphisms.

I typically use the em-dash without any further spaces because I consider it long enough to indicate a break by its own. This again is a matter of personal style. If you want to use dash to indicate pauses, omissions, and so on, please use the em-dash. It gives the eye something to follow and indicates a break. To bore you with a personal anecdote: When converting some eBooks to my Kindle, em-dashes are made into hyphens. This really confuses me when reading because I expect a compound word or a line-break but get a parenthetical remark.

In short: Dots. Dashes. Use them properly, please.