Q. If a title uses “as well as” as a conjunction meaning “and,” should it be lowercase in Chicago-style title case, as in “Apples as well as Oranges”? I’m seeing some similar book titles with “Well” capitalized, but “Apples as Well as Oranges” seems as if it could be misread.
A. First, “as well as” isn’t one of the common coordinating conjunctions named along with and in CMOS 8.160 (in rule 4). Second, even if the rule did extend to synonyms of those words, we would normally analyze the words in a phrase separately when applying title case. Accordingly, the adverb “Well” would get an initial cap, whereas the adverb/conjunction “as” would remain lowercase (per rule 5, which specifies that the word as remains lowercase in any grammatical function).
Chicago’s title-case rules, which are meant for titles mentioned in text or as part of a source citation, favor editorial expediency over aesthetic considerations. On a book cover or title page or the like, a designer may choose to de-emphasize a phrase like “as well as” by using lowercase letters or a smaller font (or both). See CMOS 8.158 for more details.
Extra credit: Starting with the 18th edition of CMOS, prepositions of more than four letters are capitalized in titles. Until then, prepositions were lowercased “regardless of length” (a clarification added to the 12th edition, published in 1969). This led some editors (including our own) to apply lowercase to phrasal prepositions like “according to,” as in “The Gospel according to Matthew,” which we’d now style as “The Gospel According to Matthew.” Not only is “according to” longer than four letters, but “according” by itself is a participle, not a preposition.