Cec Murphy is running a series on his blog for writers dealing with tips for better writing. This one is from part seven.

I know the rule even though I’m not consistent in following it—and apparently most writers aren’t either. The objection I hear from nongrammarians is, “I get tired of reading that all the time.” My answer: So revise the sentence.

Here’s the rule. That introduces an essential clause. We should play with the ball that Jack gave us. (That is, don’t use just any ball, but a specific one, the one from Jack.) We sometimes call that a restrictive element because it refers to a part of the sentence we can’t delete and keep the intended meaning.  Learn more.