Same footnote spacing than baselineskip

Question

I would like to know why exactly

\setlength{\footnotesep}{\baselineskip}

Is still not producing the same vertical spacing between footnotes than between lines inside footnotes themselves.

This is my MWE:

\documentclass[11pt,a4paper]{article}

\usepackage[a4paper,hmargin=2.5cm,vmargin={2.5cm,2.5cm}]{geometry}
\usepackage{lipsum}

% Modifier for vspace between lines (=\baselinestretch*\baselineskip)
\renewcommand{\baselinestretch}{1.5}

% Modifies the space over footnote line
\addtolength{\skip\footins}{\baselineskip}

% Modifies the space between notes in footnotes 
\setlength{\footnotesep}{\baselineskip}

\begin{document}
\lipsum[1]\footnote{\lipsum[2][1-5]}

\lipsum[2][4-7]\footnote{\lipsum[1][2-3]}

\lipsum[3][1-2]\footnote{\lipsum[3][1]}

\lipsum[4]\footnote{\lipsum[4][2-4]}
\end{document}

Which produces:

I know it is a tiny difference, almost imperceptible, but I think it can be perceived.

I guess this is relative to footnotes super index mark, which is a little upper than the top of the line.

My question actually is ... Could this be fixed with no using such an arbitrary factor as .9? Since if I use

\setlength{\footnotesep}{.9\baselineskip}

It seems to be fixed.

My idea is to have the same footnote step than line skip. Or eventually the same than paragraph skip even.

Answer 1

You should patch \footnotesize to use the normal baseline skip. Plus defining \footnotesep to be 70% of the normal baseline skip.

Here I use \regexpatch, so there is no need to copy the definition from the suitable .clo file and it works for any main size option (10pt, 11pt, 12pt) without manual intervention.

\documentclass[11pt,a4paper]{article}
\usepackage{regexpatch}

\usepackage{lipsum}

\newlength{\bodybaselineskip}
\makeatletter
\regexpatchcmd{\footnotesize}
  {(\c{footnotesize}.).*?(\c{abovedisplayskip})}
  {\1\c{bodybaselineskip}\2}
  {}{}
\setlength{\bodybaselineskip}{\normalbaselineskip}
\AtBeginDocument{\setlength{\footnotesep}{0.7\normalbaselineskip}}
\makeatother

\linespread{1.5}

\begin{document}

\lipsum[1]\footnote{\lipsum[2][1-5]}

\lipsum[2][4-5]\footnote{\lipsum[1][2-3]}

\lipsum[3][1-2]\footnote{\lipsum[3][1]}

\lipsum[4][1-5]\footnote{\lipsum[4][2-4]\the\baselineskip}\the\baselineskip

\end{document}

In case you just want to adjust the spacing between footnotes, it's less cumbersome:

\documentclass[11pt,a4paper]{article}

\usepackage{lipsum}

\linespread{1.5}
\AtBeginDocument{%
  {\footnotesize\global\footnotesep=0.7\baselineskip}%
}

\begin{document}

\lipsum[1]\footnote{\lipsum[2][1-5]}

\lipsum[2][4-5]\footnote{\lipsum[1][2-3]}

\lipsum[3][1-2]\footnote{\lipsum[3][1]}

\lipsum[4][1-5]\footnote{\lipsum[4][2-4]}

\end{document}

Or you can consider using setspace that leaves compact spacing in footnotes.

\documentclass[11pt,a4paper]{article}
\usepackage{setspace}

\usepackage{lipsum}

\setstretch{1.5}

\begin{document}

\lipsum[1]\footnote{\lipsum[2][1-5]}

\lipsum[2][4-5]\footnote{\lipsum[1][2-3]}

\lipsum[3][1-2]\footnote{\lipsum[3][1]}

\lipsum[4][1-5]\footnote{\lipsum[4][2-4]}

\end{document}

Answer 2

You are using the \baselineskip as for the regular font size but typically footnotes are set with the footnotesize font, which has a different \baselineskip.

Instead of your plain

\setlength{\footnotesep}{\baselineskip}

use

{\footnotesize \setlength{\footnotesep}{\baselineskip}}