在四种情形下使用或不使用缩略符容易引起混淆，分别是（1）复数词（2）单数所有格（3）复数所有格和（4）it's和its的缩写形式（Contractions，see cross reference hereunder）与所有格。是否使用所有格，要先问问自己是否涉及领有关系。如果是领有关系，名词或带词就要采取所有格。
规则1、Plain plural words do not require the use of an apostrophe. For example:
Incorrect: The lawyer's could generally be found after hours at the Hanover Street Bar and Grill. (The apostrophe here incorrectly indicates a singular possessive.)
Incorrect: The lawyers' could generally be found after hours at the Hanover Street Bar and Grill. (The apostrophe here incorrectly indicates a plural possessive.)
Correct: The lawyers could generally be found after hours at the Hanover Street Bar and Grill. (The lack of an apostrophe here correctly indicates a plural, nonpossessive term.)
规则2、In singular possessive terms, place the apostrophe before the "s." This will indicate ownership by one person or thing. For example:
Incorrect: Our schools collection included an original set of Blackstone's Commentaries.
Incorrect: Our schools' collection included an original set of Blackstone's Commentaries.
Correct: Our school's collection included an original set of Blackstone's Commentaries.
规则3、In plural possessive terms, place the apostrophe after the "s." This will indicate to the reader that more than one person or thing owns the thing possessed.
Incorrect: The students success was largely attributable to their hard work and dedication.
Incorrect: The student's success was largely attributable to their hard work and dedication.
Correct: The students' success was largely attributable to their hard work and dedication.
规则4、How to distinguish "its" and "it's."
"It's" is the contraction of "it is," as in the sentence, "It's best not to question the judge's knowledge of the laws of evidence in open court." In formal writing, however, one generally should not use contractions. Thus, the better formulation of the sentence above would be: "It is best not to question the judge's knowledge of the laws of evidence in open court."
"Its" is a possessive, as in the sentence, "The truck lost its muffler as it entered the pothole-laden Kennedy Expressway." This is the rare case in which a possessive term does not take an apostrophe.
规则5、A less-often faced decision involves the use of apostrophes where multiple owners are named. Where two or more people own one item jointly, place an apostrophe before an "s" only after the second-named person. For example:
Incorrect: Bill's and Mary's car was a lemon, leading them to seek rescission of their contract under the state's lemon law.
Correct: Bill and Mary's car was a lemon, leading them to seek rescission of their contract under the state's lemon law.
However, when two or more people own two or more items separately, each individual's name should take the possessive form. For example:
Incorrect: Joanne and Todd's cars were bought from the same dealer; both proved useless, even though Joanne's car was an import and Todd's was a domestic model.
Correct: Joanne's and Todd's cars were bought from the same dealer; both proved useless, even though Joanne's car was an import and Todd's was a domestic model.
规则6、When creating the possessive form of words ending in "s," use only an apostrophe after the "s" if the word ends in a "z" sound. However, if the word ends in an "s" sound use an apostrophe and an additional "s" to create the possessive.
Less Desirable: He was a student in Professor Adams's class.
More Desirable: He was a student in Professor Adams' class.
However: He was a student in Professor Weiss's class.
Cross Reference: Contractions 缩约词，通过省略或结合一个较长短语中的某些音素而形成的词，如从 will not来的 won't，或短语如从 of the clock来的 o'clock。
译注：apostrophe
省略符号, 撇号(')[用于 ①表示省略, 如:can't, (=can not); '88(=1988) ②表示所有格, 如 boy's; James' ③表示复数, 如two 0's, four 9's ④表示年代, 如the 1980's (读作 the nineteen eighties)20世纪80年代⑤表示一字中的某一音不发, 如: 'lectric (=electric)]
