Code:
\documentclass{article}
\begin{document}
Lorem ipsum dolor sit amet, pri an timeam molestiae. Dictas sententiae ius ad. Quod indoctum quo at. Et nam sale elitr, cibo solum consetetur cu cum, congue expetenda et vel. Lorem ipsum dolor sit amet, pri an timeam molestiae. Dictas sententiae ius ad. Quod indoctum quo at. Et nam sale elitr, cibo solum consetetur cu cum, congue expetenda et vel. Lorem ipsum dolor sit amet, pri an timeam molestiae. Dictas sententiae ius ad. Quod indoctum quo at. Et nam sale elitr, cibo solum consetetur cu cum, congue expetenda et vel.
\end{document}
Output (with red line numbers added):
Question: How do I increase the line spacing between (say) lines 3 & 4 and lines 4 & 5, but not between any of the other lines?
(This is not a duplicate because this other question and its answers pertain to increasing line spacing for an entire paragraph.)



\vspace. (picking the location carefully is the important thing with either method.) – barbara beeton Sep 14 '18 at 16:20\vspace{1cm}and (say)\rule[-.3\baselineskip]{0pt}{1cm}? (After reading https://tex.stackexchange.com/a/30065 I understand a little about the technical differences, but what is the practical difference?) – banbh Sep 18 '18 at 13:53