Southern Illinois University Edwardsville
URL: http://www.siue.edu/IS/WRITING/
Published by: Instructional Services Department
Last Updated: August 22, 2005 
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1.  PLURALS--The -S marker is used to indicate PLURALS, more than one thing:
            three birds                    most problems              two kinds                     some traps
            those guys                    many pencils                 several goals                 the books

2.  POSSESSION--The -S marker is used to indicate POSSESSION, which shows ownership of something.

• Belonging to one person or thing:
                          Jack's sister                  the tree's roots
                          Jill's loss                       the dog's paw
• Belonging to two or more people or things:
                          my classmates' assignment                     the Jones' house
                          three boys' boots                                  two dogs' owners
              To make a plural noun possessive, write the word and then add an apostrophe. 
              If it doesn't end in -s, add 's.
                          three neighbors' yards (Write NEIGHBORS; add '.)
                          the children's school (Write CHILDREN; add 's.)
                          the women's job (Write WOMEN; add 's.)

RULE:  Write the word that is the possessive.  If it doesn't end in -s, add 's.  If it does end in 's, add ' only.

NOTE: Personal pronouns do not use apostrophes:       The storm expended its fury.
                                                                                    The book was hers.

3.  CONTRACTIONS--Use an apostrophe in contractions:     It's a zoo in there.
                                                                                                Who's going to the dance?

Common contractions:
                        I'm (I am)         you're (you are)            they're (they are)
                        it's (it is)            we've (we have)           who's (who is)
                        he's (he is)        she's (she is)                 can't (can not)
                        isn't (is not)     couldn't (could not)      won't (will not)

4.  SUBJECT-VERB AGREEMENT--The -s marker is used to make verbs agree with singular subjects in the present tense.
                        He goes.                       She goes.                     It goes.
                        He walks.                     She walks.                    It walks.
                        He tries.                       She tries.                      It tries.

RULE: In the present tense, if the subject is a HE, SHE, or IT, then the verb must have an –s.                            Mary (she) arrives soon.
            The man (he) seems nice.
            The car (it) is damaged.