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Q. Hello! I know that spellings are always preserved in proper names. For example, in a book written in American English, “Globe Theatre” would not become “Globe Theater.” Does this extend to punctuation? In “St Thomas’s Hospital Medical School” (in London) does it stay “St” or become “St.” when mentioned in a book in American style?
A. British-style punctuation, unlike spelling, can usually be adjusted to conform to the style used in the surrounding text. This includes moving periods and commas inside closing quotation marks (and changing single quotation marks to double), replacing spaced en dashes with unspaced em dashes, and adding periods to abbreviations like “St.”—which, as a form of contraction (the first and last letters of the term are retained), isn’t normally punctuated in British style (see also CMOS 10.4).
Note, however, that the advice relative to periods does not apply to direct quotations from written sources (or, by extension, to titles of works), which should record “St Thomas’s” or “St. Thomas’s” as it appears in the source. See CMOS 13.7 for permissible changes to quotations and 8.165 for permissible changes to titles of works.