> Certainly possible, but it may have unwanted side-effects. If you settle on
> a convention like the colon in a title, you can add a \Chapter command
> (capital C) which splits off the implicit subtitle and reformats it in the
> title, keeping it out of the ToC:
>
> \documentclass{report}
> \makeatletter
> \newcommand{\Chapter}[1]{\split@chapter#1:}
> \def\split@chapter#1:#2:{\chapter[#1]{#1\\[1ex]\huge#2}}
> \makeatother
> \begin{document}
> \tableofcontents
> \Chapter{Adding Subtitles: An Extra \LaTeX\ Interpretation to Separate
> a Subtitle After a Colon}
> Stuff
> \end{document}
Why not simply use the syntax \Chapter{Title}{Subtitle}? This can be
obtained by replacing Peter's definition by
\newcommand{\Chapter}[2]{\chapter[#1]{#1\\[1ex]\huge#2}}
A full MWE heavily based on his:
\documentclass{report}
\newcommand{\Chapter}[2]{\chapter[#1]{#1\\[1ex]\huge#2}}
\begin{document}
\tableofcontents
\Chapter{Adding Subtitles}{An Extra \LaTeX\ Interpretation to Separate
a Subtitle using two arguments}
Stuff
\end{document}
///Bruno