Consecutive number of theorems, propositions, etc

Question

I'm using

\usepackage{amsthm}
\newtheorem{theorem}{Theorem}
\newtheorem{proposition}{Proposition}

The numberings of Theorem and Proposition are not consecutive (I get Theorem 1 followed by Proposition 1 instead of Theorem 1 followed by Proposition 2). How can I fix it?

I need this numbering because otherwise I would have Theorem 1, Proposition 1, Lemma 1, Corollary 1, Remark 1, etc. which I think is very confusing if I reference Proposition 1 later.

Answer 1

The \newtheorem construction offers two optional arguments. The first one fixes your numbering. In this case it means that proposition should use the same counter as theorem.

\documentclass{article}

\usepackage{amsthm}
\begin{document}


\newtheorem{theorem}{Theorem}
\newtheorem{proposition}[theorem]{Proposition}

\begin{theorem}
1+1=2.
\end{theorem}

\begin{proposition}
1+2=3
\end{proposition}

\end{document}