Enumerate function - only item 1 appearing with numbering

Question

I am having an issue with my enumerate function - only the 1st item appears to have[i] the other item doesn't have any numbering present.

\documentclass{svmono}
\begin{document}
\begin{enumerate}[i]
\item One 
\item Two 
\end{enumerate}
\end{document}

Answer 1

You need either enumerate or enumitem to support that syntax.

However, there are some problems.

Let's consider the code

\documentclass{svmono}
\usepackage{showframe}
%\usepackage{enumerate}

\begin{document}

\begin{enumerate}
\item First level
  \begin{enumerate}
    \item Second level
    \begin{enumerate}
      \item Third level
      \begin{enumerate}
        \item Fourth level
      \end{enumerate}
    \end{enumerate}
  \end{enumerate}
\item Two 
\end{enumerate}

\begin{itemize}
\item First level
  \begin{itemize}
  \item Second level
    \begin{itemize}
      \item Third level
      \begin{itemize}
        \item Fourth level
      \end{itemize}
    \end{itemize}
  \end{itemize}
\item Two 
\end{itemize}

\end{document}

Output without packages

Output after adding \usepackage{enumerate}

Output after adding \usepackage{enumitem}

Output after adding \usepackage{enumitem} with fixes.

\documentclass{svmono}
\usepackage{showframe}
\usepackage{enumitem}

\setlist[enumerate]{align=left}
\setlist[itemize]{align=left}

\begin{document}

\begin{enumerate}
\item First level
  \begin{enumerate}
    \item Second level
    \begin{enumerate}
      \item Third level
      \begin{enumerate}
        \item Fourth level
      \end{enumerate}
    \end{enumerate}
  \end{enumerate}
\item Two 
\end{enumerate}

\begin{itemize}
\item First level
  \begin{itemize}
  \item Second level
    \begin{itemize}
      \item Third level
      \begin{itemize}
        \item Fourth level
      \end{itemize}
    \end{itemize}
  \end{itemize}
\item Two 
\end{itemize}

\end{document}

Not really the same, but not so distant.

Code for your application

\documentclass{svmono}
\usepackage{showframe}
\usepackage{enumitem}

\setlist[enumerate]{align=left}
\setlist[itemize]{align=left}

\begin{document}

\begin{enumerate}[label=\roman*.]
\item One 
\item Two 
\end{enumerate}

\end{document}

Comments

The \usepackage{showframe} line has been added just to properly show the bounding box of the text block. Remove it for your document.

Using enumerate would change the appearance of all lists with respect to the svmono standard, so it is out of question. With enumitem the output is not very different.