“Chapter” before chapter number in Tufte classes

Question

Is there a way to insert usual "Chapter" before chapter number in Tufte classes, such as "Chapter 1" etc?

Answer 1

Since the tufte classes use the titlesec package, all that is needed is a small modification to \titleformat for \chapter, to include \chaptertitlename (the original definition can be found in the file tufte-common.def):

\documentclass{tufte-book}

\makeatletter
\titleformat{\chapter}%
  [display]% shape
  {\relax\ifthenelse{\NOT\boolean{@tufte@symmetric}}{\begin{fullwidth}}{}}% format applied to label+text
  {\itshape\huge\chaptertitlename~\thechapter}% label
  {0pt}% horizontal separation between label and title body
  {\huge\rmfamily\itshape}% before the title body
  [\ifthenelse{\NOT\boolean{@tufte@symmetric}}{\end{fullwidth}}{}]% after the title body
\makeatother
\setcounter{secnumdepth}{1}

\begin{document}

\chapter{Test Chapter}

\end{document}