How to create a customized paragraph?

Question

In addition to numbered and unnumbered paragraphs (section, subsection, subsubsection) I would like to have in my thesis some indented and titled paragraphs, but as paragraph command doesn't meet my needs, I'm searching for another solution. Indeed, paragraph command doesn't put enough in light the part of the text I want to emphasize. That paragraph would begin by a title such as : "Observation 1" as in the following picture : in which the paragraph that follows its title ("Observation 20") begins with an indentation different from the identation of the main body of the text.

Does anybody have a suggestion ? In the following mwe, I use an unnumbered description list in order to have an indented paragraph.

\documentclass[12pt,a4paper,footinclude=true,twoside,headinclude=true]{scrbook}
\usepackage[parts,pdfspacing,dottedtoc]{classicthesis}
\usepackage{fontspec}
\usepackage[applemac]{inputenc}    
\usepackage[frenchb]{babel}
\setmainfont{Minion Pro}
    \usepackage[marginparsep=8pt,left=3.5cm,right=3.5cm,top=3cm,bottom=3cm]{geometry}


    \begin{document}

   \begin{description}
    This is my text
   \end{description}

    \end{document}

Answer 1

You also could do that with the ntheorem package: it has a \theoremindent length,and you can define an observ theorem structure in the break style. Here is a possibility; I had to redefine the break style in order to ensure indentation for the first paragraph. If you don't want such indentation, there's nothing to redefine.

\documentclass[12pt,a4paper,footinclude=true,twoside,headinclude=true]{scrbook}
\usepackage[parts,pdfspacing,dottedtoc]{classicthesis}
\usepackage{fontspec}
\usepackage[frenchb]{babel}
\setmainfont{Minion Pro}
\usepackage[marginparsep=8pt,left=3.5cm,right=3.5cm,top=3cm,bottom=3cm]{geometry}


\usepackage{ntheorem}
\theoremindent = 3em
\theorempreskip\medskipamount
\theorempostskip\medskipamount
\theoremstyle{break}
\theoremheaderfont{\itshape}
\theorembodyfont{\normalfont}
\makeatletter
\renewtheoremstyle{break}%
 {\item[\rlap{\vbox{\hbox{\hskip\labelsep \theorem@headerfont
 ##1\ ##2\theorem@separator}\hbox{\strut}}}]\hskip\parindent}%
 {\item[\rlap{\vbox{\hbox{\hskip\labelsep \theorem@headerfont
 ##1\ ##2\ (##3)\theorem@separator}\hbox{\strut}}}]\hskip\parindent}
\makeatother
\newtheorem{observ}{Observation}

    \begin{document}

A repetitive text a repetitive text a repetitive text a repetitive text a repetitive text a repetitive text a repetitive text a repetitive text a repetitive text.
   \begin{observ}
    This is my text. This my text This is my text. This my text This is my text. This my text This is my text. This my text This is my text. This my text. This my text This is my text. This my text This is my text. This my text.

    This is my text. This my text This is my text. This my text This is my text. This my text This is my text. This my text This is my text. This my text. This my text This is my text. This my text This is my text. This my text.
   \end{observ}
 Another no less repetitive text. Another no less repetitive text. Another no less repetitive text. Another no less repetitive text. Another no less repetitive text.

    \end{document} 

Answer 2

Create your own environment to set things the way you want.

Below I've used adjustwidth (from changepage) to set a quotation-like environment called observation. The observation title follows a counter that you can reference using \label-\ref.

\documentclass{article}
\usepackage[margin=1in]{geometry}% Just for this example

\usepackage{changepage,lipsum}

\newcounter{observation}
\newenvironment{observation}
  {\par\medskip
   \begin{adjustwidth}{2em}{2em}
     \setlength{\parindent}{1.5em}% \parindent for Observations
     \small% Font changes (if any)
     \refstepcounter{observation}% Increment counter
     \hspace*{\parindent}% Indent Observation title
     Observation~\theobservation% Print Observation title
    \par\nobreak\smallskip}%
  {\end{adjustwidth}\medskip}
\begin{document}

\lipsum[1]

\begin{observation}
  \lipsum[2-3]
\end{observation}

\lipsum[4]

\begin{observation}
  \lipsum[5]
\end{observation}

\begin{observation}
  \lipsum[6]
\end{observation}

\lipsum[7]

\begin{observation}
  \lipsum[8-10]
\end{observation}

\lipsum[11]

\end{document}

You can adjust the \parindent (1.5em) and adjustwidth indents (2em) to suit your needs. The same goes for any font adjustments (\small in this case).