In a forest of commas, colons, hyphens, ampersands, pound signs, ellipses and parentheses, the apostrophe stands alone as the most misused and misunderstood of punctuation marks. It could hardly be otherwise _ apostrophes probably are used more often than any marks but periods, and their applicability dates back to Latin rules of grammar which even some English teachers may never have encountered.
Part of the confusion lies in an apostrophe's usefulness. Apostrophes are used to show possession, appearing on either side of the letter "s" according to whether the word is singular or plural. They also help form contractions. And, a while ago, purists insisted on putting an apostrophe anywhere in a word where a letter had been deleted.
The third usage probably was the earliest to vanish. It certainly was a goner by the time cartoonist Al Capp ended the 40-year run of the comic strip Li'l Abner in 1974. Under the old rule, the "Little" in Li'l Abner's name should have been written Li''l' (an apostrophe for each deleted letter). Capp followed that rule in the less successful strip Abbie an' Slats, created three years after Li'l Abner, but evidently he saw where punctuation was headed and decided one apostrophe was enough for a resident of Dogpatch. That may have been a good thing, but I doubt it. Having been freed from a rule of grammar, two generations since then have decided to ignore all logic when deleting letters in words. The effect is obvious in the world of cooking. On one on-line recipe page I found these concoctions: Pork n' Beans and Hamburger Casserole; Pork N Beans Cake; and Pork 'n' Bean Soup. That's three versions of and, shortened, plus the original "and" in all its glory.
The most frequent mistake in the use of apostrophes, though, occurs with the use of it's as a possessive pronoun. I see daily examples of this mistake _ and not just by high school sophomores. It shows up in corporate publications, advertisements, and news tickers local and national. What makes the misuse embarrassing is that "it's" is a contraction of "it is" _ the shortest complete sentence in the English language after "I am" _ and never should be used to indicate possession. "Its" (without an apostrophe) is the possessive form of the third-person, singular, neuter pronoun "it." To anyone troubled by indecision about which is which, remember: The apostrophe in it's combines two words; its without punctuation is a pronoun, used to indicate that "it" possesses something.
Now, about the uses of apostrophes where some rules still apply: Possession depends on number, meaning how many persons, places or things the noun represents.
If the noun is singular, the construction is usually simple _ the word, plus an 's at the end (the dog's collar, for instance). If plural, the apostrophe goes after the s (the dogs' collars). Of course, as usual with English, things can get complicated, especially with nouns like thesis, species or bus that end in s. The standard way to indicate possession with them was to put the apostrophe outside the last letter, but the trend in modern usage seems to be toward adding an 's, especially after common (non-capitalized) nouns. Many publications today do that while merely adding an apostrophe to the final s on a proper noun (Thomas' truck).
The one rule that seems to have remained inviolate is to never use an apostrophe when putting an s at the end of a singular noun to make it plural. In other words, never write about the Brewer's when you're talking about the Brewers, Arizona's first family.
As a former sports writer, I can't wrap this up without relating it to sports. I've always preferred team names that ended in s, but I could see the future coming when the WNBA added the Phoenix Mercury to the teams I had to cover in the Grand Canyon State. Even though it sounds singular, Mercury is a plural noun, and those who covered the team had to learn to write "Mercury's," "Mercury are" or "Mercury have," referring to their possessions, accomplishments, wins, losses or transactions. Maybe it's playing in basketball venues, but the trend went wild in the Arena Football League, where six of 14 teams have singular-sounding names. I like the Spokane Shock and Portland Thunder of the National Conference, and I'm fine with the Tampa Bay Storm, Pittsburgh Power and Philadelphia Soul of the American. I just don't know about the New Orleans VooDoo. I'd have trouble writing about the VooDoo's mojo with a straight face.