The error
appears when you give LaTeX a \ command at a time when it’s not expecting it; it is a line-breaking command, and is confused if LaTeX isn’t building a paragraph when you give the command. A common case is where you’ve decided you want the label of a list item to be on a line of its own, and written (for example):! LaTeX Error: There's no line here to end. See the LaTeX manual or LaTeX Companion for explanation.
\begin{description}
\item[Very long label] \\
Text...
\end{description}
The proper solution to the problem is to write a new sort of
description environment, that does just what you’re after. (The
LaTeX Companion
offers a rather wide selection of variants of these things.)
A straightforward solution, which avoids the warning, is to write:
\begin{description}
\item[Very long label] \leavevmode \\
Text...
\end{description}
which starts a paragraph before forcing a break. The
expdlist package provides the same functionality with its
\breaklabel command, and mdwlist provides it via its
\desclabelstyle command.
The other common occasion for the message is when you’re using the
center (or flushleft or flushright)
environment, and have decided you need extra separation between lines
in the environment:
\begin{center}
First (heading) line\\
\\
body of the centred text...
\end{center}
The solution here is plain: use the \ command in the way it’s
supposed to be used, to provide more than just a single line break
space. \ takes an optional argument, which specifies
how much extra space to add; the required effect in the text above can
be had by saying:
\begin{center}
First (heading) line\\[\baselineskip]
body of the centred text...
\end{center}
You can use \leavevmode, as above:
\begin{center}
First (heading) line\\
\leavevmode\\
body of the centred text...
\end{center}
but that is just as tiresome to type as \ with an optional
argument, and can not be recommended.
This answer last edited: 2014-01-13
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