The Apostrophe Is Your Friend - But Don't Overdo It

The apostrophe (') is often over-used.  Some folks erroneously add an apostrophe before the "s" when making a word plural.  Additionally, people will sometimes use an apostrophe with a possessive pronoun such as "its" or "theirs."

Or, sometimes people will just dispense with the apostrophe altogether, even where it's required, possibly due to uncertainty as to usage.

Keeping in mind just two very basic rules will help dissolve the confusion:

1. An apostrophe is used in contractions, in place of the missing letter or letters.
Examples: Don't (do not); you're (you are); could've (could have); it's (it is or it has); we'll (we will)

2. An apostrophe is used along with an "s" to indicate possession, except in the case of possessive pronouns like his, hers, its, ours, yours, theirs, and whose.
Examples: Bonnie's hairbrush; Florida's weather; the dog's fur

When indicating possession for more than one person or entity, make the people or entities plural before adding the apostrophe.  (A list of rules governing the use of the apostrophe can be found on this excellent site.)
Examples: "The cars' roofs were all damaged by hail." "We are going to paint the twins' bedroom."

No apostrophe is needed to pluralize words.  Merely add an "s" (or "es" or "ies") at the end, as appropriate.
Examples: Photos; toys; dresses; anniversaries

The same goes for numbers.  Just add an "s" without an apostrophe.
Examples: his 50s; the 1960s

Incorrect: "He took many photo's at the wedding." "They all had lot's of fun."  "We have celebrated many anniversary's together."
Correct: "He took many photos at the wedding." "They all had lots of fun."  "We have celebrated many anniversaries together."

Incorrect: "I dont want to go to the store." "He does'nt want to go to the store either."
Correct: "I don't want to go to the store." "He doesn't want to go to the store either."

Incorrect: "Marthas house has just been painted."  "All of the neighbors houses were painted, too."
Correct: "Martha's house has just been painted."  "All of the neighbors' houses were painted, too."