To make it easy to typeset documents with other font families (like Times Roman, Optima etc.) we maintain seven additional macros
\rmdefault \sfdefault \ttdefault \bfdefault \itdefault \scdefault \sldefaultdenoting the family chosen by
\rm, \sf, \tt or the series chosen
by \bf or the shape for \it,
\sc and \sl, respectively.6 If, for example, a document should be typeset in sans serif
one could add in the preamble (between \documentstyle
and \begin{document}) the following redefinitions:
\renewcommand{\rmdefault}{cmss}
\renewcommand{\itdefault}{sl}
The first line means that whenever \rm is called the
family cmss (i.e. computer modern sans serif) is chosen
and the second line redefines \it to switch to the slanted
shape since this family hasn't got an italic shape.
Another possible use is to say
\renewcommand{\bfdefault}{b}
This will redefine \bf to select the bold instead of the
bold extended series which is the current default.
However these commands are
probably ignored by document styles for journals which decide to
use their own font families in the final print.