Forcing new line after item number in enumerate environment

Question

How can I force the text of an enumerate item to start on a new line below the item number?

Answer 1

As egreg mentioned in a comment, using

\item\mbox{}\\

will do the job. If you want to have the job done for you automatically, you could define a command behaving like \item, but adding the \mbox{}\\:

\documentclass{article}

\makeatletter
\def\myitem{%
   \@ifnextchar[ \@myitem{\@noitemargtrue\@myitem[\@itemlabel]}}
\def\@myitem[#1]{\item[#1]\mbox{}\\}
\makeatother

\begin{document}

\begin{enumerate}
  \item\mbox{}\\First.
  \item\mbox{}\\Second.
\end{enumerate}

\begin{enumerate}
  \myitem First.
  \myitem Second.
\end{enumerate}

\end{document}

If you additionally want the item text to start left aligned with the item label, you can use the enumitem package to define a new list which behaves like a standard enumerate, but with left aligned labels; and a modification to the \myitem command from above will be necessary:

\documentclass{article}
\usepackage{enumitem}

\makeatletter
\def\myitem{%
   \@ifnextchar[ \@myitem{\@noitemargtrue\@myitem[\@itemlabel]}}
\def\@myitem[#1]{\item[#1]\mbox{}\\\hspace*{\dimexpr-\labelwidth-\labelsep}}
\makeatother

\newlist{mylist}{enumerate}{2}
\setlist[mylist,1]{align=left,label=\arabic*.}
\setlist[mylist,2]{align=left,label=(\alph*)}

\begin{document}

\begin{mylist}
  \myitem First item.
  \myitem Second item.
  \begin{mylist}
    \myitem First subitem.
    \myitem Second subitem.
  \end{mylist}
  \myitem Third item.
\end{mylist}

\end{document}