[Tex/LaTex] Left aligned section title

amsarthorizontal alignmentsectioning

I use a LaTeX template which center aligns all section titles. I want to left align these section titles but I do not know how. I tried

\begin{flushleft}
\section{\textbf{Introduction and Background}}
\end{flushleft}

but it has no effect on the section title (i.e., it is still centered). I tried 

\begin{flushleft}
\textbf{Introduction and Background}
\end{flushleft}

and it is left aligned the word "Introduction and Background" but it is no longer a section title and thus the numbering using section number are all messed up.

I am new to LaTeX so please keep it simple.

Best Answer

\documentclass{amsart}

\makeatletter
\def\specialsection{\@startsection{section}{1}%
  \z@{\linespacing\@plus\linespacing}{.5\linespacing}%
%  {\normalfont\centering}}% DELETED
  {\normalfont}}% NEW
\def\section{\@startsection{section}{1}%
  \z@{.7\linespacing\@plus\linespacing}{.5\linespacing}%
%  {\normalfont\scshape\centering}}% DELETED
  {\normalfont\scshape}}% NEW
\makeatother

\begin{document}

\section{Introduction and Background}

\end{document}

Note that using formatting macros within section titles as in

\section{\textbf{Introduction and Background}}

is not the recommended way to make general changes. You should rather use

\normalfont\scshape\bfseries

in the definition of \section (and make sure to use a font that provides bold small capitals).

Also see What do \makeatletter and \makeatother do?

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