Type styles are specified by three independent components. If a font (the combination of these three components) is chosen which is not available, LaTeX will issue a warning and substitute a similar font.
declaration command
\mdseries \textmd Medium Series
\bfseries \textbf Boldface Series
\rmfamily \textrm Roman Family
\sffamily \textsf Sans Serif Family
\ttfamily \texttt Typewrite Family
\upshape \textup Upright Shape
\itshape \textit Italic Shape
\slshape \textsl Slanted Shape
\scshape \textsc Small Caps Shape
\normalfont \textnormal Normal Style
The \normalfont declaration sets series, family, and shape to
the main text font of the document.
When using the Typewriter Family, words will be hyphenated only where permitted by a \- command.