Question: I am using BibLaTeX with backend biber and philosopy-modern as style. What I am looking for: I want the subtitles of books, collections etc. in the bibliography to appear in upright font, i.e. not in italics as the maintitle.

Some months ago I found a solution (if I am right I redefined the title in the main document via `\renewbibmacro*{title ...}`), but inadvertently I now changed some characters and I can't remember how to reestablish my definition. What I had not done was to copy `\newbibmacro*{title ...}`, redefine it between `\makeatletter` and \makeatother simly by removing `[titlecase]` in front of `{subtitle}` (at least it doesn't work any longer).

Does anybody have any idea?
(I don't attach an example, because the problem remains the same with other biblatex-styles, different biber-options, redefinitions of various parts of the `biblatex.def` ...)

Answer: 
In the following example, I modified the `title` bibmacro as desired. Note that similar changes should be applied to the `booktitle`, `maintitle`, `journal`, `periodical`, and `issue` bibmacros (all located in `biblatex.def`).

Addendum: The modification is not obvious - it's only a closing brace removed from one code line and added to another. The effect is that `\printfield[titlecase]{subtitle}` isn't (anymore) part of the argument of `\printtext[title]`.

```
\documentclass{article}

\usepackage{biblatex}

\renewbibmacro*{title}{%
  \ifboolexpr{
    test {\iffieldundef{title}}
    and
    test {\iffieldundef{subtitle}}
  }
    {}
    {\printtext[title]{%
       \printfield[titlecase]{title}%
%       \setunit{\subtitlepunct}% DELETED
%       \printfield[titlecase]{subtitle}}% DELETED
       \setunit{\subtitlepunct}}% NEW
     \printfield[titlecase]{subtitle}% NEW
     \newunit}%
  \printfield{titleaddon}}

\usepackage{filecontents}

\begin{filecontents}{\jobname.bib}
@misc{A01,
  author = {Author, A.},
  year = {2001},
  title = {Alpha},
  subtitle = {An introduction},
}
\end{filecontents}

\addbibresource{\jobname.bib}

\nocite{*}

\begin{document}

\printbibliography

\end{document}

```

![enter image description here](https://i.stack.imgur.com/DpUVl.jpg)
In the end I has to redefine the title and remove titlecase in the definition of subtitle.

That's what I did (and it works though it doesn't look very professional)

```
\renewbibmacro*{title}{%
   \ifboolexpr{
     test {\iffieldundef{title}}
     and
     test {\iffieldundef{subtitle}}
  }
  {}
{\printtext[title]{%
   \printfield[titlecase]{title}%
   \setunit{\subtitlepunct}%
   \printfield{subtitle}}%
 \newunit}%
 \printfield{titleaddon}}

 \renewbibmacro*{booktitle}{%
   \ifboolexpr{
      test {\iffieldundef{booktitle}}
     and
     test {\iffieldundef{booksubtitle}}
   }
     {}
   {\printtext[booktitle]{%
   \printfield[titlecase]{booktitle}%
   \setunit{\subtitlepunct}%
   \printfield{booksubtitle}}%
 \newunit}%
   \printfield{booktitleaddon}}

 \renewbibmacro*{maintitle}{%
   \ifboolexpr{
 test {\iffieldundef{maintitle}}
and
test {\iffieldundef{mainsubtitle}}
  }
{}
{\printtext[maintitle]{%
   \printfield[titlecase]{maintitle}%
   \setunit{\subtitlepunct}%
   \printfield{mainsubtitle}}%
 \newunit}%
 \printfield{maintitleaddon}}

 \renewbibmacro*{journal}{%
  \iffieldundef{journaltitle}
{}
{\printtext[journaltitle]{%
   \printfield[titlecase]{journaltitle}%
   \setunit{\subtitlepunct}%
   \printfield{journalsubtitle}}}}

 \DeclareFieldFormat[book, thesis, online, collection,
 proceedings, journal]{subtitle}{\textnormal{#1}}
\DeclareFieldFormat[collection,
proceedings]{mainsubtitle}{\textnormal{#1}}
\DeclareFieldFormat{booksubtitle}{\textnormal{#1}}
\DeclareFieldFormat{journalsubtitle}{\textnormal{#1}}

```