I followed previous examples on here, but could not eliminate the newline after the subsubsection (I want it to runin just like paragraph does)
\documentclass[oneside,openany,openbib,11pt]{memoir}
\usepackage{titlesec}
\titleformat{\subsubsection}[runin]{\bfseries}{}{}{}[]
\titleformat{\paragraph}[runin]{\normalsize\itshape}{}{}{}[]
\begin{document}
\subsection{testing}
blah blah blah
\subsubsection{subtesting}\paragraph{further testing}blah blah blah
\end{document}
\paragraph
starts a new paragraph anyway.\paragraph
is not the command you want to use. Define your own