# Why is redefining a command erring? [closed]

I am trying to redefine \emph to bold its argument:

\renewcommand\emph[1]{{\textbf{\oldemph{#1}}}}


However, after typing this command before begin{document}, I get an error every time I use \emph{Some text.}: Undefined control sequence.

What is a control sequence? How do I fix my redefinition?

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## closed as not a real question by doncherry, Kurt, Andrew Swann, Stefan Kottwitz♦Oct 29 '12 at 6:26

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Can you provide a minimal working example (MWE) that reproduces your error? –  user2473 Oct 29 '12 at 1:54
How did you define \oldemph? –  Mico Oct 29 '12 at 1:55
@cmhughes's answer solves my problem and has a working example. Sorry, I will make sure to provide an MWE in the future. –  David Faux Oct 29 '12 at 2:00
@DavidFaux glad it helped- my code is an example of a complete MWE :) –  cmhughes Oct 29 '12 at 2:02

The following works for me

\documentclass{article}

\let\oldemph\emph
\renewcommand\emph[1]{{\bfseries{\oldemph{#1}}}}

\begin{document}

\emph{hello world}
\end{document}

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