I have a question that is similar to How can I make a custom theorem for a definition? and also to Custom theorem numbering italicized, but I'm not able to work out how to do it from these. My wish is the following:

define a custom theorem style so that the body of the text is slanted via \textsl{...} (not italicised via \textit{...}).

For example, I would like it to look like this.

\textbf{Theorem 1.1} (theorem name)\textbf{.} \textsl{Statement of theorem.}

This link https://en.wikibooks.org/wiki/LaTeX/Theorems#Custom_styles should also be helpful, but again I am unable to make it work myself.

Advice on how to do this would be most appreciated, thanks.

I'm using packages amsmath and ntheorem. I've no particular attachment to the package ntheorem: if changing to use a different package would make it easier, then I don't think this would mess up my other stuff.

  • A point of terminology: \textsl produces "slanted", not "italicized", text.
    – Mico
    Commented Mar 1, 2018 at 15:13
  • Do you use a theorem-related package such as amsthm or ntheorem? Please advise.
    – Mico
    Commented Mar 1, 2018 at 15:14
  • I have both, yes. I'm perfectly happy to add another package if necessary. (And thanks for the terminology!)
    – Sam OT
    Commented Mar 1, 2018 at 15:22
  • There is a difference between italic and slanted, but is that really important?
    – user31729
    Commented Mar 1, 2018 at 15:25
  • 1
    @Mico: I am aware that the difference depends on the font. It's most likely Miconificant ;-)
    – user31729
    Commented Mar 1, 2018 at 15:38

2 Answers 2


(edited the answer after the OP provided more information about the desired appearance of the theorem-like environment.

I would like to suggest that you use the amsthm package and define a new theorem style, called sltheoremstyle in the example below.

enter image description here


{}                % Space above
{}                % Space below
{\slshape}        % Theorem body font % (default is "\upshape")
{}                % Indent amount
{\bfseries}       % Theorem head font % (default is \mdseries)
{.}               % Punctuation after theorem head % default: no punctuation
{ }               % Space after theorem head
{}                % Theorem head spec

Hello World. 
  • Apologies for not making it clearer, but I don't want the "Theorem #" to be slanted, but bold as it originally is. If you see my update, hopefully this will clarify. Just removing \theoremheaderfont{\slshape} from your commands doesn't work either, since it then makes the optional argument bold, eg Theorem 1 (name) rather than Theorem 1 (name).
    – Sam OT
    Commented Mar 1, 2018 at 15:58
  • @SamT - I've updated my answer to incorporate the additional information you provided.
    – Mico
    Commented Mar 1, 2018 at 16:21
  • Ah, silly me, I read amsthm as amsmath! Apologies about that. Your answer now looks exactly as I thought it would, I just wasn't exactly what inputs to use. (I assume all yours are the default, eg 1em after theorem head, except that you've put in \slshape?)
    – Sam OT
    Commented Mar 1, 2018 at 16:24
  • @SamT - To use the default settings for any one of the options, simply leave the corresponding argument blank.
    – Mico
    Commented Mar 1, 2018 at 16:29
  • Ah ok, thanks :) -- do you happen to know what the default for 'space after theorem head' is?
    – Sam OT
    Commented Mar 1, 2018 at 16:30

Bad typography (slanted) ahead...




\newtcbtheorem{slantedtheorem}{Theorems from hell}{colback=yellow!20!white,colbacktitle={yellow!40!white},coltitle={black},fontupper=\slshape,fonttitle={\slshape}}{sltheo}

\begin{slantedtheorem}{I am slanted}{ohmy}

enter image description here

  • 1
    That would certainly draw the reader's attention!
    – Sam OT
    Commented Mar 1, 2018 at 16:32
  • 1
    @Mico: My first idea was Typography from hell ;-)
    – user31729
    Commented Mar 1, 2018 at 16:39

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