Titles become 'unbolded' when adding in a new theoremstyle

Question

Up until now, whenever I create a new definition or theorem etc., the title (so the word 'Definition' etc.) would come up in bold. However, when I try to add '\theoremstyle{remark}', the titles stop coming up in boldface. Is there any way I can fix this (i.e. so I don't have to bold each title individually as it comes up)? Sorry if this is a stupid question, I'm very new to all this.

Answer 1

You should use them like this.

\documentclass{article}
\usepackage{amsmath,amsthm}

\newtheorem{theorem}{Theorem}[section]
\newtheorem{corollary}{Corollary}[section]
\newtheorem{proposition}{Proposition}[section]
\newtheorem{lemma}{Lemma}[section]
\newtheorem{example}{Example}[section]
\theoremstyle{definition}
\newtheorem{definition}{Definition}[section]
\theoremstyle{remark}
\newtheorem{remark}{Remark}[section]
\begin{document}
  \begin{definition}
    This is a definition
  \end{definition}
  \begin{theorem}
    This is a theorem
  \end{theorem}
  \begin{corollary}
    This is a corollary
  \end{corollary}
  \begin{proposition}
    This is a proposition
  \end{proposition}
  \begin{lemma}
    This is a lemma
  \end{lemma}
  \begin{example}
    This is an example
  \end{example}
  \begin{remark}
    This is a remark
  \end{remark}
\end{document}