then.
Part A: As an Adjective.
“Then” should not be hyphenated when alone as an adjective meaning “that existed or was so at that time” {the then mayor of San Diego}. But when the word is part of a phrasal adjective, the phrase should be hyphenated {then-mayor Rudolph Giuliani}, but not after {Rudolph Giuliani, then mayor of New York, said . . .}
Part B: For “than.”
This is a distressingly common error, especially in newsprint — e.g.: “He enjoyed much more autonomy with ‘Face/Off’ then [read ‘than’] he did with his other movies.” Douglas J. Rowe, “Director Woo Puts a New Face on American Family Values,” Salt Lake Trib., 4 July 1997, at C8. Language-Change Index — “then” misused for “than”: Stage 1.
For information about the Language-Change Index click here.
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Quotation of the Day: “Try to make the quotation a part of your own work; introduce it in your own words; substitute your own paraphrase when it becomes prolix; steel yourself to junking the best passage unless it is relevant; chop up the rest and throw away the remains.” Sherman Kent, Writing History 66 (1941).