[Tex/LaTex] Textsuperscript does not work with letters

Question

An attempt to write 8th

8\textsuperscript{th} resulted in the same text 8th

while the same environment worked well with numbers

8\textsuperscript{8} and produced correct view with subscript.

Why does textsuperscript not work with letters?
P.S. Math mode is not used due to inattractive font view

MWE

\documentclass[11pt,notitlepage,oneside,openany,a5paper]{book} 
\usepackage{geometry}  
\geometry{a5paper}
\begin{document}
8\textsuperscript{th}
\\
8\textsuperscript{1}
\end{document}

Answer 1

Please always post complete documents that show the problem. It should work:

\documentclass{article}

\begin{document}

8\textsuperscript{th} 8th

\end{document}