Could'a, would'a, should'a.

We know it's OK to use contractions in speech, but when should they be used in writing?

Until the early 20th century, most teachers treated contractions like cockroaches scuttling and hissing through students' sentences. These fuming pedagogues fumigated, ordering students never to use contractions. Of course, they were also ordering them never to buckle their knickers above the knee.

Since then, teachers and usage authorities have chilled. Most of them now advise us to embrace our inner apostrophe and use contractions where they seem to blend naturally with the rhythm and tone of the sentence.

As William Zinsser advised in "On Writing Well," "Your writing style will be warmer and truer to your own personality if you use contractions like 'won't' and 'can't' when they fit comfortably into what you're writing."

While it's true that contractions can impart a friendly, authentic tone to your prose, don't be too casual. Your goal in using contractions, advises grammar guru Bryan Garner, should be to convey "relaxed sincerity," not breeziness.

As Rudolf Flesch wrote, "Contractions have to be used with care. Sometimes they fit, sometimes they don't."

So, when deciding whether to use a contraction, consider the context and purpose of your writing, and, most of all, your audience. Writing to a colleague, "I hadn't known about the Bunkerby project, but I'll be glad to help with whatever you've decided," is one thing.

But writing to your boss, "As you'll see in the attached memo, the negative ramifications of the Throckmorton merger aren't minor and shouldn't be ignored" might seem too informal. Using "you will see," "are not minor," and "should not be ignored" would impart the appropriate emphasis and gravity.

But, even in informal contexts, be careful. Some contractions that sound fine in speech should be avoided in writing because they're rendered so awkwardly in print: she'd've, I'd've, there're, it'd, who're.

Likewise, be careful of two common errors involving contractions:

— Adding a needless "-'ve" to the conditional past perfect. "If I'd've gone to the concert," for example, should be "If I'd gone to the concert."

— Writing "of" for the spoken "have," as in "I should of known" for "I should've known."

— Contracting "is" with a noun. This is dangerous because the noun might be misread at first as a possessive, e.g., "The teacher's itching to kill that cockroach!

Rob Kyff, a teacher and writer in West Hartford, Conn., invites your language sightings. Send your reports of misuse and abuse, as well as examples of good writing, via e-mail to [email protected] or by regular mail to Rob Kyff, Creators Syndicate, 737 3rd Street, Hermosa Beach, CA 90254.