Unless you fell down a Google rabbit hole and ended up here unintentionally, you’re probably already aware just how much information is contained in the AMA Manual of Style. But to put it in perspective, the style guide’s current iteration contains 1010 pages, and that’s not counting the pages at the very beginning that are numbered with Roman numerals (because no one reads those anyway, right? [sorry Cheryl]). Still, despite the borderline-unmanageable amount of information in the AMA Manual of Style, the articles I edit on a day-to-day basis are usually very sound regarding obscure rules found 3 bullet points below a niche subsection of information explaining…you-name-it. I can generally count on authors to italicize gene names and keep corresponding proteins unitalicized or to capitalize virus terms that end in -virales, -viridae, or -virinae, etc.
But the cost of the attention to the more complicated nuances of AMA style seems to be that baseline grammatical rules get overlooked. I’m not saying that the articles that hit my desk are anarchically grammarless, but there are usually at least 1 or 2 hard-and-fast grammatical conventions that get ignored. And the rule that gets violated far and beyond all the others pertains to the usage of the relative pronouns “that” and “which.”
So here’s a quick refresher for everyone (myself included): A restrictive clause directly affects the intended meaning of the subject in the preceding clause, and restrictive clauses are introduced by “that.” Nonrestrictive clauses are not necessary to the intended meaning of the subject in the preceding clause, and nonrestrictive clauses are introduced by “which.”
Example of a restrictive clause: The band The National wrote a song that is my favorite song. Because “that is my favorite song” modifies the subject “song” to a degree essential for the intended meaning, a restrictive clause introduced with “that” is necessary (the subject “song” would not be the particular song in question—my favorite song—if the restrictive clause wasn’t present). The modified subject’s intended meaning hinges on the restrictive clause.
Example of a nonrestrictive clause: The band The National wrote a song called “The Geese of Beverly Road,” which is a perfect example of early-00’s indie-rock songwriting. Because “which is a perfect example…” simply describes the subject “song” and doesn’t change its intended meaning, all that’s required is a nonrestrictive clause introduced with “which.” The modified subject would still be the song in question (“The Geese of Beverly Road”) in this context without the information the nonrestrictive clause provides.
I know, I know, this seems to be a nitpicky issue that no one save the professional manuscript editor would get hung up on, but precision with language hinges on attention to grammatical detail, which is crucial when presenting scholarly research and information.—Sam Wilder