# \bar vs. \overline - when to use what, semantically?

Following the question "The \bar and \overline commands" which is simply about the lengths of both, I'd like to know when to use \bar and when to use \overline from a semantically viewpoint.

I always used \bar, because up until now I only had single letter mean values to type. But now I came to a problem where I needed a wider "bar".

Then I just tried

\documentclass{article}

\begin{document}
$\bar{a} \overline{a}$
$\bar{abc} \overline{abc}$
\end{document}


where one can see that they also differ in position (\overline is lower), and also in thickness (\overline is thicker).

So, the question here is:

What does \bar represent semantically? And when to choose it over \overline and vice versa?

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For wider bars you can use my \widebar command (shameless plug). – Hendrik Vogt Feb 13 at 14:27

Semantically, don't use either. Use \conj, or \mean, or \variant or whatever the overline is meant to mean. Then in your preamble, do:

\newcommand*\conj[1]{\bar{#1}}
\newcommand*\mean[1]{\bar{#1}}


Then:

1. Your document source becomes readable: you can determine the meaning right there and then.
2. Your document becomes more flexible: if you decide to denote complex conjugation by a star instead you can simply redefine \conj without worrying about changing what \mean does.
3. You can change from \bar to \overline on a whim and don't have to make that crucial decision now.
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while the suggestion to use a "meaningful" command is excellent, the expansion would have to be more complicated to allow for single or multiple-letter arguments. since the original question mentioned both, that should be addressed in your answer. – barbara beeton Feb 13 at 22:22

\bar{a} can mean just "another thing" like if you used a' or \tilde{a} or \diamondclub. You never use \overline for this.

However, if you denote an operation like complex conjugation, reversal, set closure or whatever, you can use whichever you want. You found out that somehow (to some people) \bar{a} seems "too subtile" for this purpose, and you can use the reasonable solution proposed in the other question. This goes along the fact that in this case, things like \overline{x+y}, \overline{2U+V}, \overline{a_1a_2 dots a_n} have their meaning as well.

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