LaTeX error · Commands, braces and arguments

Paragraph ended before \author was complete.

Q: How do I put several authors in \author without a blank line?

Separate them with \and, which sets them side by side, or with \\ for a new line. Affiliations can go on the next line after \\ or in \thanks{...}.

Q: Is this error the same as Runaway argument?

They come together. Runaway argument? shows the argument TeX was reading; Paragraph ended before ... was complete is the error that stopped it.

Quick answer

Some LaTeX commands refuse a paragraph break inside their argument. When TeX meets a blank line (or \par) while reading the argument of the command named in the message, it stops with this error. Either there really is a blank line inside the argument, for example between two authors in \author{...}, or the closing } is missing so the argument ran into the next paragraph. Remove the blank line (use \and or \\ to separate lines) or add the brace.

The error in the log

This is how the message appears in the .log file (and in the compile output). The line starting with l. is the line number where TeX noticed the problem; the real mistake is there or just before it.

Runaway argument?
{Ada Lovelace 
! Paragraph ended before \author  was complete.
<to be read again> 
                   \par 
l.5

Why it happens

A blank line used to separate authors or affiliations in \author{...} or \title{...}.
A blank line or missing } in \label, \ref or \cite (reported as \label, \@citex@checkblank or similar).
A two-paragraph \caption, reported as Paragraph ended before \addcontentsline was complete because the caption text is also written to the list of figures.
A macro you defined with \newcommand*, whose arguments may not contain paragraphs.

How to fix it

Read the command name in the message and the text after Runaway argument?, which is the start of the argument. Remove the blank line inside it. Separate several authors with \and, and break lines inside a title or author block with \\.

Recent LaTeX releases let \textbf, \section and most formatting commands contain paragraphs, so a missing brace there is reported later as File ended while scanning use of ... instead.

Broken: reproduces the error

\documentclass{article}

\title{A Study of Braces}
\author{Ada Lovelace

Charles Babbage}

\begin{document}
\maketitle
\end{document}

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Fixed: compiles cleanly

\documentclass{article}

\title{A Study of Braces}
\author{Ada Lovelace \and Charles Babbage}

\begin{document}
\maketitle
\end{document}

Related errors

Runaway argument – A command argument that never ends: its closing brace is missing.
Missing } inserted – A brace group was still open when math mode or a table cell ended.
There's no line here to end – A \\ or \newline where no line of text has started.
All LaTeX errors and warnings – The full list, grouped by cause

Frequently Asked Questions

How do I put several authors in \author without a blank line?

Separate them with \and, which sets them side by side, or with \\ for a new line. Affiliations can go on the next line after \\ or in \thanks{...}.

Why does a caption give Paragraph ended before \addcontentsline was complete?

The caption contains a blank line. Captions are copied to the list of figures, which cannot take a paragraph break. Remove the blank line, or use \caption[Short entry]{Long caption} and keep the long text to a single paragraph.

Is this error the same as Runaway argument?

They come together. Runaway argument? shows the argument TeX was reading; Paragraph ended before ... was complete is the error that stopped it.

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