# About memoir and titlesec incompatibility

In page 2 of the titlesec documentation, Javier Bezos writes

titlesec works with the standard classes and with many others, including the AMS ones, and it runs smoothly with hyperref. Unfortunately, it is not compatible with memoir, which provides its own tools with a limited subset of the features available in titlesec.

I don't use the memoir document class so I am not familiar with its features, but I've made a few simple tests (really few and simple) using it together with titlesec and couldn't detect any problems. To what extent can titlesec be safely used with memoir? Which exactly are the incompatibilities mentioned?

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See this answer here Examples of styles for section headings for a parallel quote from the memoir manual. As I understand it, they're not really incompatible, but you can't really mix and match their respective ways of redefining the sectioning commands. –  Alan Munn Oct 29 '11 at 1:22
memoir defines sectioning commands with two optional arguments and this will be lost with titlesec. –  egreg Oct 29 '11 at 12:37
@egreg: but something like \usepackage{titlesec}\titleformat{\chapter}[display] {\normalfont\huge\itshape}{\chaptertitlename\ \thechapter}{20pt}{\Huge} will still allow using the two optional arguments of \chapter. –  Gonzalo Medina Nov 4 '11 at 16:20
As long as you consistently use only titlesec commands for specifying titles, you should have no problems with memoir. But you cannot mix and match. –  Seamus Nov 4 '11 at 17:51
I have brought this thing up with the memoir maintainer and asked to replace memoir's rather limited algorithms with those of titlesec. Unfortunately, he wouldn't listen... The titlesec way of doing things is far superior to the may memoir does it. But I still use memoir since it is getting a long way in the right direction. –  user43153 Dec 24 '13 at 0:51

For chapters the incompatibility is not evident, as \titleformat{\chapter}... will redefine \@makechapterhead and \@makeschapterhead. However

\documentclass{memoir}
\usepackage{titlesec}

will redefine \section in such a way that the second optional argument is not accepted; indeed