The font commands like \small, \tiny, \footnotesize are not commands with arguments. They apply within the entire scope containing them. If you want to limit their application, you either need to use the environment \begin{small} ... \end{small}, or else put the \small command
inside an extra pair of braces, like so: {\small Text}.
So in your case, maybe you want something like this:
Code: Select all
\documentclass{article}
\usepackage{xspace}
\newcommand\seize{{\small XVI}\textsuperscript{\tiny e}\xspace}
\begin{document}
Normal {\footnotesize blabkblbalbablablabl \seize century} Normal
\end{document}
(I couldn't even the command you gave, however, since I don't know how "\up" is defined, and since you had \} instead of } at the end, the number of braces was mismatched. A true
minimal working example is always most helpful.)