Q. I am writing a government report, and the first letters of words in the title are supposed to be capitalized. In such a case, should prepositions be capitalized? The government employee who edited my work said that along should be capitalized, but not of, and this doesn’t make any sense to me.
A. As of the 18th edition of CMOS, prepositions of more than four letters get an initial cap in Chicago-style title case (see paragraph 8.160). And some styles (notably AP) cap any preposition that’s longer than three letters. So your editor wasn’t off base.