Nonbreakable space for bibliography

Question

Why do we need to use a nonbreakable space ~ for the bibliography?

For example, in the book "More math into LaTeX" by G. Grätzer, on pp. 47, the following snippet of code is given:

\bibitem{eM57a}
Ernest~T. Moynahan,
\emph{Ideals and congruence relations in
lattices.} II,
Magyar Tud. Akad. Mat. Fiz. Oszt. K\"{o}zl.
\textbf{9} (1957), 417--434.

As far as I can see, using a ~ for names in the bibliography does not make sense, as names never get so long that they would be broken - in contrast for references for theorem numbers and the like, where the 2 from Theorem 2 indeed might end up on the next line, if this was typeset as Theorem \cite{sometheorem}.

Answer 1

In the book "Practical LaTeX" of George Grätzer you can find on page 94 a simular example like that you showed in your question.

\begin{thebibliography}{9}
\bibitem{gM12}%
  George~A. Mennuhin, \emph{Universal Algebra},
  University Series in Higher Mathematics, vol.~158,
  D.~Van Nostrand, Princton, 2012.
\end{thebibliography}

Here the vol.~158 and D.~Van can make sense because with the usage of \bibitem the writer of the document has the control for a good layout.

I teach my students (for didactical reasons) always write a ~ where one do not want to get a line break, if it is useless (George~A. a linebreak should not occur) or not. It is easier to write ~ always than only from time to time where it is needed.

If the bibliography is build via .bib file I do not write ~.

With the following MWE (I doubled the \bibitem to have one with ~, one without)

\documentclass[11pt]{article} % try with 10pt and 11pt

\usepackage[left=3cm,right=3cm,showframe]{geometry}

\begin{document}
Text~\cite{gM12} Text \cite{gM13} text

\begin{thebibliography}{9}
  \bibitem{gM12}%
    George~A. Mennuhin, \emph{Universal Algebra},
    University Series in Higher Mathematics, vol.~158,
    D.~Van Nostrand, Princton, 2012.
  \bibitem{gM13}%
    George A. Mennuhin, \emph{Universal Algebra},
    University Series in Higher Mathematics, vol. 158,
    D. Van Nostrand, Princton, 2012.
\end{thebibliography}

\end{document}

I get the resulting pdf:

Marked with the red arrow you can see an usually unwanted line break between vol. and number 158. With other parameters for geometry or fontsize you can get the situation, that a typographic unwanted line break could happen between D. and Van. So I think it makes sense writing ~ in bibliographys build with \bibitem ...