[Tex/LaTex] subtitle or titleaddon: which to choose

biblatex

Question

In my .bib file, I want to add a book that has a "main" and a "subsidiary" title.

Which field should I use for the subsidiary title: titleaddon or subtitle? (The biblatex documentation is not clear enough on that point for me – cf. ยง2.2.2 on page 23.)
What is the difference between the two in practice?


Example

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Considering previous book, which of following entry is the most indicated (changes in the penultimate line only) ?

@Book{Williams2002,
 Title                    = {Free as in Freedom},
 Author                   = {Williams, Sam},
 Publisher                = {O'Reilly Media},
 Year                     = {2002},
 ISBN                     = {0-596-00287-4},
 Titleaddon               = {Richard Stallman's Crusade for Free Software}
}

or

@Book{Williams2002,
 Title                    = {Free as in Freedom},
 Author                   = {Williams, Sam},
 Publisher                = {O'Reilly Media},
 Year                     = {2002},
 ISBN                     = {0-596-00287-4},
 Subtitle                 = {Richard Stallman's Crusade for Free Software}
}

Best Answer

The main difference between subtitle and titleaddon is the presentation in the bibliography. While subtitle is set in the same style as the title and connected by a special \subtitlepunct, titleaddon is (by default, you can of course change that) set in normal font. This can make one feel that titleaddon is not as closely connected to the title as subtitle.

Indeed in biblatex-examples.bib you will find titleaddon used to add a description like "Proceedings of the ...". The example files to biblatex-chicago use titleaddon either as a replacement for a proper title or to provide additional information such as "review of ..." or "interview with ...".

All in all, I would say that the titleaddon is often used in a "meta" capacity to give additional information or to replacing a missing title. subtitle on the other hand is mostly on the same level as title.

In your case then, I would probably go for subtitle, but that is just my gut feeling.