Using Apostrophes Correctly - A Primer

Apostrophes are used in several contexts. In certain very limited circumstances they are used to make plural forms of words. They are used to make contractions of two words into one. Most frequently in formal writing, apostrophes are used to show possessiveness.

Plurals

Apostrophes do not make a word plural. Ever. If you mean to indicate more than one of a person, place or thing, just add s or es to the word:

dishes
phones
pens
blogs

Sometimes we see numbers with apostrophes. Some sources approve this style, but the better practice is to avoid it.

The MLA Handbook, which is the Bible of American punctuation, instructs us not to add apostrophes to pluralize even numbers written numerically:

Olga Korbut scored unprecedented 10s from the gymnastics judges.
Music during the 1990s was unremarkable for the most part.

When the number is spelled out as a word, it is made plural just like any other word. Add only the letter s with no apostrophe:

She was dressed to the nines.
Throughout the nineties I listened to classical rock most often.

Even if it is the plural of an acronym or abbreviation, do not use the apostrophe to make a plural:

Both of us have IRAs.
He has PhDs in both English and Philosophy.
Please return the DVDs to Blockbuster.

This rule having been fully explained, I shall now confuse you by telling you that there are some authorities which say that using an apostrophe to make the plural of letters or numbers, as well as words referred to as words in the context of the sentence, is acceptable. Both formats are correct, so long as the writer is consistent.

There are no if's, and's or but's about it.
There are no ifs, ands, or buts about it.

Shakespeare wrote plays during the 1500's and 1600's.
Shakespeare wrote plays during the 1500s and 1600s.

Those size 14's make his feet look like longboats.
Those size 14s make his feet look like longboats.

Jack had three C's on his report card.
Jack had three Cs on his report card.