“Grammar saves lives,” says one meme. Another admonishes, “don’t be a psycho; use a comma!” Compare “Let’s eat, Grandma!”to “Let’s eat Grandma!” and you’ll have a laugh—and see how misplaced punctuation can change the meaning of a sentence.

Aside from social media sharing, though, grammar and usage rules don’t generally elicit a happy response. Frequently they’re seen as rigid structures created by curmudgeonly editors to make the lives of writers miserable. While editors may indeed be curmudgeonly about the rules, they’re actually trying to make things easier for both writers and readers. With National Grammar Day approaching on March 4, It’s the perfect time to ask ourselves why exactly these rules exist?and what they can do for us.

Clarity

Many of the much-maligned grammar and punctuation rules developed out of the need for clarity of meaning. The “Let’s eat, Grandma” joke above is just one example, but clarity of meaning goes beyond a simple punctuation mark. Take, for example, the words complimentary and complementary; the first means free of charge (or refers to the act of offering a compliment), while the second implies that things work together well. The words are frequently used interchangeably, but this misuse could engender disappointment or worse:

Example A: Complimentary paintings adorn the hotel room. This means that the paintings are free—so pop one in your suitcase.

Example B: Complementary paintings adorn the hotel room. This, however, means that the paintings go well with, or match, the decor in the room. It doesn’t mean they’re free, so if you were to take a painting, you might be arrested—and lack of knowledge of grammar isn’t a great defense in court.

Not all grammatical rules create such drastic situations, but most exist to make sure that the reader understands exactly what You’re trying to say.

Consistency

One big issue for editors is consistency, or treating like situations alike. For example, in a book involving internal monologue and regular dialogue, the internal monologue should always be formatted the same way (e.g. italicized, if that’s what the author and editor decide). Why? Inconsistency in style and usage can create confusion, but even if the meaning is still clear, inconsistency can be jarring to the reader. A distracted reader is one who’s less likely to “get” the message or story you’re trying to communicate, which means that your whole purpose of writing may be undermined.

Content

The final major reason for grammar and style conventions is content. When Marshall McLuhan wrote, “The medium is the message,” he may have been referring to the differences between media like print and television, but the concept goes deeper to cover tone and style. Different purposes of communication require different levels of formality; adjusting the grammatical and usage rules to fit the occasion can affect the way the writing is perceived. Just like a three-piece suit blends in well at a formal party but would look silly on at the beach, so does formal language seem out of place in, say, dialogue between teens. On the other hand, full sentences and parallel structure give the impression of an organized mind—so when you’re applying for a job or writing a thesis paper, matching the grammatical style with the occasion is just as important as making sure you’re professionally dressed for your interview or dissertation.

Far from being an obnoxious set of norms imposed by cranky editors, writing rules are there to ensure that your readers understand what You’re trying to tell them. Writing’s all about communication between you and the reader—and grammatical rules and style conventions are the key to making that communication happen.

Christina M. Frey is a book editor and a lover of great writing. Chat with her on Twitter about all things literary @turntopage2.