Change subsubsection to medium series

Question

I am using Lyx on Windows. How do I get the formatting of the whole document to look like:

\subsubsection{\textmd{Blah blah blah}}

without manually setting it for each line?

Answer 1

If you want to only change the text:

\let\OriginalSubsubsection\subsubsection%
\renewcommand{\subsubsection}[1]{\OriginalSubsubsection{\textmd{#1}}}%

As per Stefan's suggestion if you also want to also adjust the numbering:

\let\OriginalTheSubsubsection\thesubsubsection
\renewcommand{\thesubsubsection}{\textmd{\OriginalTheSubsubsection}}

Answer 2

You can use the titlesec package to format any sectional command. For example, obtaining a medium formatting for \subsubsection use

\usepackage{titlesec}% http://ctan.org/pkg/titlesec
...
\titleformat{\subsubsection}{\mdseries}{\thesubsubsection}{1em}{}%

In a more general setting, the respective arguments of \titleformat is

\titleformat{<command>}[<shape>]{<format>}{<label>}{<sep>}{<before-code>}[<after-code>]

Note that optional arguments are specified using [...], while mandatory arguments use {...}. Consequently, in the above redefinition of \subsubsection, <format>=\mdseries for medium font, <label>=\thesubsubsection to print the number of the sub-subsection, <sep>=1em to provide a space of 1embetween thesub-subsection title, and` is also empty. Play around with these settings to see what fits you, or leave a comment.

Finally, read the package documentation for more information on the details of each component.