How to mark titles
Works whose titles I would mark fall into two groups.
First are 'the heavyweights', pieces of a certain length and importance books - factual or fiction; plays; films; journals and newspapers; operas; major poems, of a length over, say, 50 pages titles of sequences, e.g. of song-cycles, paintings and poems etc (other pieces of work with similar characteristics)
Second are smaller pieces, often component parts of members of the first group. These include: chapters of books; articles in Journals; short poems; songs in operas; song titles; short stories; individual pictures etc (other less 'weighty' pieces).
The precise memberships of these groups is largely a matter of judgement and taste. In general, try to adapt your practice to a consistent view of what constitutes a long and what a short piece of work. Over time, it will change; and there will always be borderline cases which will be disputed by pedants (try your best not to join in too seriously!).
The first group, the heavy weights, should be marked more strongly. Different publishers and Departments in Universities etc have different 'house rules' for this, so follow the expectations of the audience you are writing for. My practice is always to use italics when word-processing. (Traditionally the manuscript, or handwriting, equivalent of italic was underlining. This acted as an instruction to a printer to set the type as italic. In modern word-processing, where italic is as easy as, if not easier than, underlining, I prefer it. It is after all the ultimate effect that was always intended.) In handwriting, which was not intended for a printer, for example school essays and private letters, the tradition was to use double quotation marks. These were preferred over single quotation marks, because they were less ambiguous. See quotation marks.)
The most usual practice nowadays to mark the second sort of title (the 'lightweight' ones), is to use single quotation marks. So we might get: "The chapter 'Airs and Graces' in Lynne Truss's book on punctuation, Eats, Shoots and Leaves...", or "The song 'Voi che sapete' [the Italian song 'You who Know'] in Mozart's Figaro...", or "Meron's article, ' The Geneva Conventions as Customary Law' in The American Journal of International Law."
See also: Titles - of books, etc..
