5 writing rules that change across style guides

3 min read

If you’re not a published writer you may not be familiar with the concept of a style guide. But even if your to-do lists and journal entries aren’t being published, you can benefit from a style guide. A style guide is basically a glossary of rules to follow when writing. It establishes guidelines for how to write numbers, titles, addresses, punctuation, and anything else that could vary.

But even with a style guide, there are no hard and fast rules in the English language. There are multiple versions of style guides, and the rules for common situations can vary from guide to guide. That’s right — none of these style guides are exactly the same, which raises plenty of questions and leads to many a linguistic debate. No one seems to agree on what’s correct, but that’s only because each style guide applies to a different situation — and none of them are wrong.

A style guide for everyone

Any publication can create their own style guide, but there are a few style guides published by reputable sources that most publications follow. Or they use one of the established guides as a starting point and write a few specialized rules unique to their purposes.

The Chicago Manual of Style is used widely for nonfiction writing. It includes the standard guidelines for punctuation and word usage, but its most valuable resource is the citation guidelines. It gives clear rules for formatting your citations and bibliography.

The Associated Press (AP) Stylebook is most commonly used by news organizations. However, it’s such a clear reference for rules regarding grammar, punctuation, capitalization, abbreviation, spelling, and numerals that it’s been adopted by many industries outside of the media.

The last major style guide is the Modern Language Association (MLA) Handbook. It contains the same categories of rules as the other ones, but is most commonly used by students and for academic writing.

There are plenty more specialized guides, such as APA, used mostly for science writing, but unless you're in a particular industry, these three should cover most of your style guide needs.

Though these are the three most commonly referenced guides, there are a few things they disagree on. Here are a few rules that vary across the different style guides.

Serial comma

The serial comma, also known as the Oxford comma, is the comma that comes between the second-to-last item in a list and a conjunction. For example, “blue, red, and yellow.” The comma after red is the serial comma, but some styles argue shouldn’t be there at all.

Chicago Style includes the serial comma, while AP style has historically rejected it. The good thing is that some degree of its use comes down to personal preference. If you’re not writing a scholarly paper or official document, you’re probably safe either way. Just pick a style and stick with it.

Em dash

The Chicago and MLA style guides both say no spaces between the em dash and the words beside it, while AP says there should be spaces.

Chicago and MLA: He burnt the bacon to a crisp—just how I like it.

AP: He burnt the bacon to a crisp — just how I like it.

Do these spaces change the meaning? Nope! But it’s a formatting rule that should remain consistent, no matter which guideline you follow.

Title rules

Title rules can be a little tricky. Some styles use italics, some capitalize differently, and sometimes it comes down to what type of document you’re titling.

Chicago and MLA are similar in their titling rules. They use lowercase letters for all prepositions, and they use italics for the entire title. APA and AP styles use quotation marks instead of italics, and they capitalize prepositions longer than three words. For example:

Chicago and MLA: A Room with a View

AP and APA: “A Room With a View”


It’s an old argument. Do you use apostrophe + s or just an apostrophe hanging on at the end of the word ending in s? Once again, both are correct. It just depends on style, and in some cases, whether the noun is plural.

For a singular noun ending in s (boss, octopus, mess), AP and Chicago use an apostrophe + S. APA and MLA use just the apostrophe. However, if the noun is plural and ends in s (bosses, octopuses, messes), all styles use an apostrophe only.


Some styles say to spell out numbers. Others say to write the numeral itself. AP style says to spell out any number less than 10, while Chicago takes this rule all the way up to 100. MLA is stranger still, with its rule that says spell out any number if it can be written in one or two words. That means that one million should be written out, but 672 is written like so.

If all of these changing rules confuse you, don’t worry. You’re not alone. That’s why we have style books. And if you don’t want to look up someone else’s rules, just write your own!

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