Shorter space after ellipsis

Question

MWE

Is this true? expected? typographically correct? If it should be fixed, how? I've browsed related questions but found no answers.

\documentclass[10pt]{article}

\usepackage[text={2.1in,4in}]{geometry}

\usepackage{microtype} % since it's in my document

\begin{document}

In this sentence the space after the ellipsis \dots seems
noticeably shorter than the space before it. 

\end{document}

Answer 1

barbara's answer explains why this happens and offers some advice on how to address it. I have to say, I'm pretty sure I'm wildly inconsistent about how I handle this.

Here's a comparison:

\documentclass{article}

\begin{document}
Some words \dots after the beginning.

Some words \textellipsis after the beginning.

Some words \dots\ after the beginning.

Some words \textellipsis\ after the beginning.
\end{document}

produces:

While the lack of space in the first two cases looks odd, the second two don't look quite right to me either because the space after the ellipsis now exceeds that before it.

As I understand it, this is because space equal to that between the dots is added after the final dot to ensure that any following punctuation is correctly spaced:

Do you know some words \dots?

Do you know some words \textellipsis?

produces:

which seems reasonable. When \ is added after the ellipsis, the additional space is added to the space already there.

If you want even spacing around the ellipsis, the ellipsis package offers a solution:

\documentclass{article}
\usepackage{ellipsis}
\begin{document}

Some words \dots\ after the beginning.

Some words \textellipsis\ after the beginning.

Do you know some words \dots?

Do you know some words \textellipsis?
\end{document}

produces balanced spacing in both kinds of case:

But if, like me, you are horribly inconsistent about this, you might hope the package would solve the problem automatically.

According to the documentation, you should be able to do just this using the option xspace. In that case, you are supposed to be able to type \dots whatever and have everything work. However, when I try that, the spacing after the ellipsis is again larger than that before it, although the effect is less pronounced than without the package.

That is,

\documentclass{article}
\usepackage[xspace]{ellipsis}
\begin{document}

Some words \dots\ after the beginning.

Some words \textellipsis\ after the beginning.

Some words \dots after the beginning.

Some words \textellipsis after the beginning.

Do you know some words \dots?

Do you know some words \textellipsis?
\end{document}

produces

rather than

So I'm not sure this option works quite as intended....

EDIT Moreover, xspace's author recommends avoiding the package.

Answer 2

there's no space after \dots because spaces after a control sequence are ignored (except as needed to recognize the end of the control sequence).

the usual recommendation is to insert a "slash space" after \dots\ to get an ordinary (as opposed to end-of-sentence) space. however, if \dots really does end a sentence, then entering it as \dots{} or {\dots} will trigger the end-of-sentence space.

\dots can appear in contexts where it's not possible to determine whether it should be followed by a space in the output, or indeed, what kind of space.

edit: after reading the excellent answer by cfr, i decided to do a little digging. the definitions of \dots in both plain tex and latex are somewhat convoluted, but the point about the extra space being added to \dots (and \textellipsis} to ensure good spacing before another punctuation mark is right on.

what i discovered, though, is that, even though \dots and \textellipsis share this feature in text mode, \ldots (on which both are based) is free from it, as shown in this simple demonstration.

\documentclass[12pt]{article}
\begin{document}
\fbox{.}\quad\fbox{.\,.}\quad\fbox{\dots}\quad\fbox{$\ldots$}
\end{document}

so, if your goal is absolutely symmetrical spaces before and after the dots, use \ldots directly. (in other words, don't be la{tex}zy.)

on another tack, in a comment someone asked about using the unicode character (U+2026) directly. when implemented in a font, that character is usually designed (in most fonts that i've seen) with tighter spacing than provided by \dots and would look out of place in most tex settings.