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

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

When to use each of them?

\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 \em is not an outdated TeX or LaTeX2.09 command but a real LaTeX2e command.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}

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])

\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}

To get a more indepth description see wikibooks and texfaq. Let me present what is there in a condensed form, because I think the origin of misusing \em and \emph comes from not knowing how they help specifying a font.

## Font Specification Now

Specification of a font works by choosing a series, a shape, a family and a size. You can choose from 3 series, 4 shapes and 3 families: One of

• \bfseries,\mdseries,\lfseries switches to the series,
• \upshape,\itshape,\slshape,\scshape switches to the shape,
• \rmfamily,\sffamily,\ttfamily switches to the family.

Enclosing the text in braces makes it to a TeX group, thus restores the previous series/shape/family at closing brace. If you choose a slanted or italic shape you have to apply an italic correction (\/). You can use the non-switch version of these: Take the first two letters and appent "text", this is the name of an ordinary command that works as expected i.e. either acts on a single char or on a text enclosed in braces.

## Font Specification Then

Before LaTeX2e there were only switch like statements like \bf,\tt,\em. They modified the text as long as no other was encountered. This is why \em{abc}de gives "abcde": {abc} is just a group, since no different switch is ancountered \em does not stop working at the closing brace. \it I\bf like \it\bf fresh air gives "I like fresh air".

## emph & em

Well... sorry for the overhead. \em is different in that it not really is a switch to italics like \it/\itshape. It just switches from upright/small-capitals to italics or from italics/slanted to upright when it is encountered (switches the shape) and leaves the family and series untouched. Thus the definition of \emph should be losely equivalent to \def\emph#1{\/{\em#1}\/}. Which works as expected:
{\upshape a\emph{b\emph{c\emph{d}e}f}g} yields "a b c d e f g" (without the spaces of course). The Implemetation in LaTeX2e is of course different, they use \DeclareTextFontComand{\emph}{\em} which does a similar thing but also checks for mathmode.

The most imporatant thing is the Implementation of \em in LaTeX2e which is indeed such that the behaviour as said above: {\scshape Aha \em Aha \em Aha} yields "AHA Aha Aha" where the AHA is in small capitals (the scshape ist not restored after the 2nd \em).

From what I understood, em is the TeX command and emph is its LaTeX equivalent. Therefore, you should use the emph when using LaTeX.

• \em is a plain tex command, not something defined by the engine. it requires you to write your own italic correction commands, which \emph works out for you. – wasteofspace Aug 17 '11 at 8:52
• Neither \em nor \emph are defined in plain.tex. – user3143179 Nov 21 '16 at 22:07