# What is the difference between \em and \emph?

What is the difference between \emph{...} and {\em ...}?

When to use each of them?

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Take a look at: tex.stackexchange.com/q/11199/86 as well. –  Loop Space Aug 17 '11 at 8:02

\emph is like e.g. \textit a command with an argument. \em is the "switch" variant, comparable to \itshape. \em is not an outdated TeX or LaTeX2.09 command but a real LaTeX2e command. Actually \emph is defined through em:

\DeclareTextFontCommand{\emph}{\em}


\em is useful for long texts (\emph e.g. doesn't allow the argument to contain a \par). The commands differ (like the \textit/\itshape) in their handling of the italic correction:

\documentclass{article}
\begin{document}

abc\emph{lll}lll  \textit{lll}llll

abc{\em lll}lll  {\itshape lll}llll

abc{\em lll\/}lll

%\emph{abc\par bc} error

{\em abc\par bc}
\end{document}


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l2tabu (a guide to obsolete commands and packages, available in English and, more up-to-date, in German) comments on \em as follows:

May be useful when defining macros. In continuous text \emph{...} should be preferred to \em.

(Table 1, p. 8 [en] / 10 [de])

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\emph is a LaTeX2e command and \em is a LaTeX 2.09 declaration, see e.g. http://www.public.asu.edu/~rjansen/latexdoc/emph.html . Since you're probably using LaTeX2e you should use \emph.

• \emph is a command and is used like \emph{text}.
• \em is a declaration and is used like \em text or {\em text}.

Their differences may be demonstrated by the following:

\documentclass{article}

\begin{document}

some \em text% Works as intended

some {\em text}% Works as intended

some \em{text}% Does not work as intended, "text" is not emphasized

some \emph{text}% Works as intended

some \emph text% Does not work as intended, only "t" of "text" is emphasized

\end{document}

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From what I understood, em is the TeX command and emph is its LaTeX equivalent. Therefore, you should use the emph when using LaTeX.
@Anon: This clashes with what @Ulrike is saying in her answer. Calling it an equivalent is definitely inappropriate because of the different usage: {\em Text} vs. \emph{Text}. –  doncherry Aug 17 '11 at 9:30